diff --git a/cmd/maleeni/lex.go b/cmd/maleeni/lex.go
index 142f996..d31ab17 100644
--- a/cmd/maleeni/lex.go
+++ b/cmd/maleeni/lex.go
@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"io/ioutil"
 	"os"
-	"time"
 
 	"github.com/nihei9/maleeni/driver"
 	"github.com/nihei9/maleeni/spec"
@@ -13,7 +12,6 @@ import (
 )
 
 var lexFlags = struct {
-	debug        *bool
 	source       *string
 	output       *string
 	breakOnError *bool
@@ -32,7 +30,6 @@ your lexical specification that is set passively, lexemes in that mode will not
 		Args:    cobra.ExactArgs(1),
 		RunE:    runLex,
 	}
-	lexFlags.debug = cmd.Flags().BoolP("debug", "d", false, "enable logging")
 	lexFlags.source = cmd.Flags().StringP("source", "s", "", "source file path (default stdin)")
 	lexFlags.output = cmd.Flags().StringP("output", "o", "", "output file path (default stdout)")
 	lexFlags.breakOnError = cmd.Flags().BoolP("break-on-error", "b", false, "break lexical analysis with exit status 1 immediately when an error token appears.")
@@ -45,30 +42,6 @@ func runLex(cmd *cobra.Command, args []string) (retErr error) {
 		return fmt.Errorf("Cannot read a compiled lexical specification: %w", err)
 	}
 
-	var opts []driver.LexerOption
-	if *lexFlags.debug {
-		fileName := "maleeni-lex.log"
-		f, err := os.OpenFile(fileName, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
-		if err != nil {
-			return fmt.Errorf("Cannot open the log file %s: %w", fileName, err)
-		}
-		defer f.Close()
-		fmt.Fprintf(f, `maleeni lex starts.
-Date time: %v
----
-`, time.Now().Format(time.RFC3339))
-		defer func() {
-			fmt.Fprintf(f, "---\n")
-			if retErr != nil {
-				fmt.Fprintf(f, "maleeni lex failed: %v\n", retErr)
-			} else {
-				fmt.Fprintf(f, "maleeni lex succeeded.\n")
-			}
-		}()
-
-		opts = append(opts, driver.EnableLogging(f))
-	}
-
 	var lex *driver.Lexer
 	{
 		src := os.Stdin
@@ -80,7 +53,7 @@ Date time: %v
 			defer f.Close()
 			src = f
 		}
-		lex, err = driver.NewLexer(clspec, src, opts...)
+		lex, err = driver.NewLexer(clspec, src)
 		if err != nil {
 			return err
 		}
diff --git a/driver/lexer.go b/driver/lexer.go
index 03540e3..bce8d8c 100644
--- a/driver/lexer.go
+++ b/driver/lexer.go
@@ -7,7 +7,6 @@ import (
 	"io/ioutil"
 	"strings"
 
-	"github.com/nihei9/maleeni/log"
 	"github.com/nihei9/maleeni/spec"
 )
 
@@ -146,17 +145,6 @@ func DisableModeTransition() LexerOption {
 	}
 }
 
-func EnableLogging(w io.Writer) LexerOption {
-	return func(l *Lexer) error {
-		logger, err := log.NewLogger(w)
-		if err != nil {
-			return err
-		}
-		l.logger = logger
-		return nil
-	}
-}
-
 type Lexer struct {
 	clspec          *spec.CompiledLexSpec
 	src             []byte
@@ -168,7 +156,6 @@ type Lexer struct {
 	tokBuf          []*Token
 	modeStack       []spec.LexModeID
 	passiveModeTran bool
-	logger          log.Logger
 }
 
 func NewLexer(clspec *spec.CompiledLexSpec, src io.Reader, opts ...LexerOption) (*Lexer, error) {
@@ -186,7 +173,6 @@ func NewLexer(clspec *spec.CompiledLexSpec, src io.Reader, opts ...LexerOption)
 			clspec.InitialModeID,
 		},
 		passiveModeTran: false,
-		logger:          log.NewNopLogger(),
 	}
 	for _, opt := range opts {
 		err := opt(l)
@@ -194,57 +180,36 @@ func NewLexer(clspec *spec.CompiledLexSpec, src io.Reader, opts ...LexerOption)
 			return nil, err
 		}
 	}
-	l.logger.Log("Initializing the lexer finished.")
 
 	return l, nil
 }
 
 func (l *Lexer) Next() (*Token, error) {
-	l.logger.Log(`lexer#Next():
-  State:
-    mode: #%v %v
-    pointer: %v
-    token buffer: %v`, l.Mode(), l.clspec.ModeNames[l.Mode()], l.srcPtr, l.tokBuf)
-
 	if len(l.tokBuf) > 0 {
 		tok := l.tokBuf[0]
 		l.tokBuf = l.tokBuf[1:]
-		l.logger.Log(`  Returns a buffered token:
-    token: %v
-    token buffer: %v`, tok, l.tokBuf)
 		return tok, nil
 	}
 
 	tok, err := l.nextAndTransition()
 	if err != nil {
-		l.logger.Log("  Detectes an error: %v", err)
 		return nil, err
 	}
-	l.logger.Log("  Detects a token: %v", tok)
 	if !tok.Invalid {
-		l.logger.Log(`  Returns a token:
-    token: %v
-    token buffer: %v`, tok, l.tokBuf)
 		return tok, nil
 	}
 	errTok := tok
 	for {
 		tok, err = l.nextAndTransition()
 		if err != nil {
-			l.logger.Log("  Detectes an error: %v", err)
 			return nil, err
 		}
-		l.logger.Log("  Detects a token: %v", tok)
 		if !tok.Invalid {
 			break
 		}
 		errTok.match = errTok.match.merge(tok.match)
-		l.logger.Log("  error token: %v", errTok)
 	}
 	l.tokBuf = append(l.tokBuf, tok)
-	l.logger.Log(`  Returns a token:
-    token: %v
-    token buffer: %v`, errTok, l.tokBuf)
 
 	return errTok, nil
 }