diff --git a/.github/workflows/lint.yaml b/.github/workflows/lint.yaml
index a49285d..6b7a1a8 100644
--- a/.github/workflows/lint.yaml
+++ b/.github/workflows/lint.yaml
@@ -22,4 +22,4 @@ jobs:
     - name: golangci-lint
       uses: golangci/golangci-lint-action@v3
       with:
-        version: v1.46.2
+        version: v1.52.2
diff --git a/.go-version b/.go-version
index b9fb27a..5fb5a6b 100644
--- a/.go-version
+++ b/.go-version
@@ -1 +1 @@
-1.18.3
+1.20
diff --git a/Dockerfile b/Dockerfile
index 991346a..4fd0995 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,5 +1,5 @@
 # build
-FROM golang:1.18.3-alpine3.16 AS builder
+FROM golang:1.20-alpine3.17 AS builder
 RUN apk --no-cache add make git
 WORKDIR /work
 
@@ -13,7 +13,7 @@ RUN make build
 # The linux binary for hub can not run on alpine.
 # So we need to build it from source.
 # https://github.com/github/hub/issues/1818
-FROM golang:1.18.3-alpine3.16 AS hub
+FROM golang:1.20-alpine3.17 AS hub
 RUN apk add --no-cache bash git
 RUN git clone https://github.com/github/hub /work
 WORKDIR /work
@@ -22,7 +22,7 @@ RUN ./script/build -o bin/hub
 # runtime
 # Note: Required Tools for Primary Containers on CircleCI
 # https://circleci.com/docs/2.0/custom-images/#required-tools-for-primary-containers
-FROM alpine:3.16
+FROM alpine:3.17
 RUN apk --no-cache add bash git openssh-client tar gzip ca-certificates
 COPY --from=builder /work/bin/hcledit /usr/local/bin/
 COPY --from=hub /work/bin/hub /usr/local/bin/
diff --git a/README.md b/README.md
index 770a489..62f826d 100644
--- a/README.md
+++ b/README.md
@@ -36,7 +36,7 @@ https://github.com/minamijoyo/hcledit/releases
 
 ### Source
 
-If you have Go 1.18+ development environment:
+If you have Go 1.20+ development environment:
 
 ```
 $ git clone https://github.com/minamijoyo/hcledit
diff --git a/cmd/version.go b/cmd/version.go
index d0296be..2f93a89 100644
--- a/cmd/version.go
+++ b/cmd/version.go
@@ -25,7 +25,7 @@ func newVersionCmd() *cobra.Command {
 	return cmd
 }
 
-func runVersionCmd(cmd *cobra.Command, args []string) error {
+func runVersionCmd(cmd *cobra.Command, _ []string) error {
 	_, err := fmt.Fprintln(cmd.OutOrStdout(), Version)
 	return err
 }
diff --git a/go.mod b/go.mod
index 39eed56..0386f49 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/minamijoyo/hcledit
 
-go 1.18
+go 1.20
 
 require (
 	github.com/hashicorp/hcl/v2 v2.12.0
diff --git a/main.go b/main.go
index ad954b9..7be1db2 100644
--- a/main.go
+++ b/main.go
@@ -3,7 +3,6 @@ package main
 import (
 	"fmt"
 	"io"
-	"io/ioutil"
 	"log"
 	"os"
 
@@ -25,7 +24,7 @@ func logOutput() io.Writer {
 	minLevel := os.Getenv("HCLEDIT_LOG")
 
 	// default log writer is null device.
-	writer := ioutil.Discard
+	writer := io.Discard
 	if minLevel != "" {
 		writer = os.Stderr
 	}
diff --git a/main_test.go b/main_test.go
index d65ac08..2af34cc 100644
--- a/main_test.go
+++ b/main_test.go
@@ -154,7 +154,7 @@ func argsToEnv(args []string) []string {
 func envToArgs(env []string) []string {
 	var envvars []string
 
-	for _, kv := range os.Environ() {
+	for _, kv := range env {
 		if strings.HasPrefix(kv, VarRunMainForTestingArgPrefix) {
 			envvars = append(envvars, kv)
 		}