diff --git a/mackerel.go b/mackerel.go
index cbf8696..704ab32 100644
--- a/mackerel.go
+++ b/mackerel.go
@@ -24,6 +24,10 @@ type Client struct {
 	UserAgent         string
 	AdditionalHeaders http.Header
 	HTTPClient        *http.Client
+
+	// Logger specifies an optional logger.
+	// If nil, logging is done via the log package's standard logger.
+	Logger *log.Logger
 }
 
 // NewClient returns new mackerel.Client
@@ -40,7 +44,7 @@ func NewClientWithOptions(apikey string, rawurl string, verbose bool) (*Client,
 	}
 	client := &http.Client{}
 	client.Timeout = apiRequestTimeout
-	return &Client{u, apikey, verbose, defaultUserAgent, http.Header{}, client}, nil
+	return &Client{u, apikey, verbose, defaultUserAgent, http.Header{}, client, nil}, nil
 }
 
 func (c *Client) urlFor(path string) *url.URL {
@@ -69,10 +73,15 @@ func (c *Client) buildReq(req *http.Request) *http.Request {
 func (c *Client) Request(req *http.Request) (resp *http.Response, err error) {
 	req = c.buildReq(req)
 
+	logPrintf := log.Printf
+	if c.Logger != nil {
+		logPrintf = c.Logger.Printf
+	}
+
 	if c.Verbose {
 		dump, err := httputil.DumpRequest(req, true)
 		if err == nil {
-			log.Printf("%s", dump)
+			logPrintf("%s", dump)
 		}
 	}
 
@@ -83,7 +92,7 @@ func (c *Client) Request(req *http.Request) (resp *http.Response, err error) {
 	if c.Verbose {
 		dump, err := httputil.DumpResponse(resp, true)
 		if err == nil {
-			log.Printf("%s", dump)
+			logPrintf("%s", dump)
 		}
 	}
 	if resp.StatusCode < 200 || resp.StatusCode > 299 {
diff --git a/mackerel_test.go b/mackerel_test.go
index ad9fa60..e16b2d1 100644
--- a/mackerel_test.go
+++ b/mackerel_test.go
@@ -1,8 +1,11 @@
 package mackerel
 
 import (
+	"bytes"
+	"log"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
 )
 
@@ -57,3 +60,20 @@ func TestBuildReq(t *testing.T) {
 		t.Errorf("X-Revision should be '%s' but %s", xRev, h)
 	}
 }
+
+func TestLogger(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(res http.ResponseWriter, req *http.Request) {
+		res.Write([]byte("OK"))
+	}))
+	defer ts.Close()
+
+	client, _ := NewClientWithOptions("dummy-key", ts.URL, true)
+	var buf bytes.Buffer
+	client.Logger = log.New(&buf, "<api>", 0)
+	req, _ := http.NewRequest("GET", client.urlFor("/").String(), nil)
+	client.Request(req)
+	s := strings.TrimSpace(buf.String())
+	if !strings.HasPrefix(s, "<api>") || !strings.HasSuffix(s, "OK") {
+		t.Errorf("verbose log should match /<api>.*OK/; but %s", s)
+	}
+}