diff --git a/build.gradle b/build.gradle
index 04490aa..52db858 100644
--- a/build.gradle
+++ b/build.gradle
@@ -29,6 +29,8 @@ dependencies {
     compile  "com.treasuredata.client:td-client:0.9.0"
 
     testCompile "junit:junit:4.+"
+    testCompile "org.embulk:embulk-standards:0.9.12"
+    testCompile "org.embulk:embulk-core:0.9.12:tests"
 }
 
 task classpath(type: Copy, dependsOn: ["jar"]) {
diff --git a/src/main/java/org/embulk/input/td/writer/DoubleValueWriter.java b/src/main/java/org/embulk/input/td/writer/DoubleValueWriter.java
index f2fdc5a..1a2edb3 100644
--- a/src/main/java/org/embulk/input/td/writer/DoubleValueWriter.java
+++ b/src/main/java/org/embulk/input/td/writer/DoubleValueWriter.java
@@ -13,6 +13,13 @@ public DoubleValueWriter(final Column column) {
 
     @Override
     public void writeNotNull(final Value v, final PageBuilder to) {
-        to.setDouble(index, v.asFloatValue().toDouble());
+        if (v.isFloatValue()) {
+            to.setDouble(index, v.asFloatValue().toDouble());
+        } else if (v.isStringValue()) {
+            // Support for DECIMAL type, which is packed / unpacked as String type in msgpack
+            to.setDouble(index, Double.parseDouble(v.asStringValue().toString()));
+        } else {
+            to.setNull(index);
+        }
     }
 }
diff --git a/src/test/java/org/embulk/input/td/TestTdInputPlugin.java b/src/test/java/org/embulk/input/td/TestTdInputPlugin.java
index e7a8975..397f297 100644
--- a/src/test/java/org/embulk/input/td/TestTdInputPlugin.java
+++ b/src/test/java/org/embulk/input/td/TestTdInputPlugin.java
@@ -1,4 +1,127 @@
 package org.embulk.input.td;
 
+import static org.embulk.spi.type.Types.BOOLEAN;
+import static org.embulk.spi.type.Types.DOUBLE;
+import static org.embulk.spi.type.Types.JSON;
+import static org.embulk.spi.type.Types.LONG;
+import static org.embulk.spi.type.Types.STRING;
+import static org.embulk.spi.type.Types.TIMESTAMP;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assume.assumeNotNull;
+
+import java.util.ArrayList;
+import java.util.List;
+import org.embulk.EmbulkTestRuntime;
+import org.embulk.config.ConfigDiff;
+import org.embulk.config.ConfigSource;
+import org.embulk.config.TaskReport;
+import org.embulk.config.TaskSource;
+import org.embulk.input.td.TdInputPlugin;
+import org.embulk.spi.InputPlugin;
+import org.embulk.spi.PageOutput;
+import org.embulk.spi.Schema;
+import org.embulk.spi.TestPageBuilderReader.MockPageOutput;
+import org.embulk.spi.util.Pages;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Rule;
+import org.junit.Test;
+
+
 public class TestTdInputPlugin {
+    private static String EMBULK_TD_TEST_APIKEY;
+    private static String EMBULK_TD_TEST_DATABASE;
+
+    /**
+     * This test case requires environment variables:
+     *   EMBULK_TD_TEST_APIKEY
+     *   EMBULK_TD_TEST_DATABASE
+     * If the variables not set, the test case is skipped.
+     */
+    @BeforeClass
+    public static void initializeConstantVariables() {
+        EMBULK_TD_TEST_APIKEY = System.getenv("EMBULK_TD_TEST_APIKEY");
+        EMBULK_TD_TEST_DATABASE = System.getenv("EMBULK_TD_TEST_DATABASE");
+        assumeNotNull(EMBULK_TD_TEST_APIKEY, EMBULK_TD_TEST_DATABASE);
+    }
+
+    @Rule
+    public EmbulkTestRuntime runtime = new EmbulkTestRuntime();
+
+    private ConfigSource config;
+    private InputPlugin runner;
+    private MockPageOutput output;
+
+    /**
+     * Initialize the config, runner, and output
+     * Note: "query" needs to be updated in each test case
+     */
+    @Before
+    public void createResources() {
+        config = runtime.getExec().newConfigSource()
+                .set("type", "td")
+                .set("apikey", EMBULK_TD_TEST_APIKEY)
+                .set("database", EMBULK_TD_TEST_DATABASE)
+                .set("query", "");
+        runner = new TdInputPlugin();
+        output = new MockPageOutput();
+    }
+
+    @Test
+    public void primitiveTest() {
+        String primitiveQuery =
+                   "SELECT * FROM ( VALUES ( "
+                   + "BOOLEAN 'true', "
+                   + "INTEGER '0', "
+                   + "BIGINT '1', "
+                   + "DOUBLE '0.0', "
+                   + "DECIMAL '0.5', "
+                   + "VARCHAR '0123' "
+                   + " ) )";
+        Schema schema = Schema.builder()
+                   .add("col_boolean",   BOOLEAN)
+                   .add("col_integer",   LONG)
+                   .add("col_bigint",    LONG)
+                   .add("col_double",    DOUBLE)
+                   .add("col_decimal",   DOUBLE)
+                   .add("col_varchar",   STRING)
+                   .build();
+
+        ConfigSource config = this.config.deepCopy().set("query", primitiveQuery);
+        ConfigDiff configDiff = runner.transaction(config, new Control(runner, output));
+
+        List<Object[]> records = Pages.toObjects(schema, output.pages);
+        assertEquals(1, records.size());
+        {
+            Object[] record = records.get(0);
+            assertEquals(true, record[0]);
+            assertEquals(0L, record[1]);
+            assertEquals(1L, record[2]);
+            assertEquals(0.0, record[3]);
+            assertEquals(0.5, record[4]);
+            assertEquals("0123", record[5]);
+        }
+    }
+
+    static class Control
+            implements InputPlugin.Control {
+        private InputPlugin runner;
+        private PageOutput output;
+
+        Control(InputPlugin runner, PageOutput output) {
+            this.runner = runner;
+            this.output = output;
+        }
+
+        @Override
+        public List<TaskReport> run(TaskSource taskSource, Schema schema, int taskCount) {
+            List<TaskReport> reports = new ArrayList<>();
+            for (int i = 0; i < taskCount; i++) {
+                reports.add(runner.run(taskSource, schema, i, output));
+            }
+            return reports;
+        }
+    }
 }