diff --git a/LICENSE b/LICENSE
index 5ccb3e9..ab75d54 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2018 Nao YONASHIRO
+Copyright (c) 2019 Nao YONASHIRO
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
diff --git a/rget.sh b/rget.sh
index 7102654..d90a4c0 100755
--- a/rget.sh
+++ b/rget.sh
@@ -1,22 +1,52 @@
 #!/bin/sh
 set -e
-WORKDIR=`mktemp -d`
 
+URL=
+OUTPUT=
 PROCESS=4
-BLOCKSIZE=8388608
-while getopts "P:b:o:u:" OPTION
+BLOCK_SIZE=
+
+usage() {
+    echo "Usage: rget.sh -o OUTPUT -u URL [-P PROCESS] [-b BLOCK_SIZE]" >&2
+}
+
+while getopts "o:u:P:b:" OPTION
 do
-  case $OPTION in
-    P) PROCESS=${OPTARG};;
-    b) BLOCKSIZE=${OPTARG};;
+  case ${OPTION} in
     o) OUTPUT=${OPTARG};;
-    *) exit $E_OPTERROR;;
+    u) URL=${OPTARG};;
+    P) PROCESS=${OPTARG};;
+    b) BLOCK_SIZE=${OPTARG};;
+    *) usage; exit 2;;
   esac
 done
-shift $(($OPTIND - 1))
 
-CONTENT_LENGTH=`curl -IsSL -X GET $1 | grep Content-Length: | awk '$0=$2'`
-echo $CONTENT_LENGTH
-seq 0 $BLOCKSIZE $CONTENT_LENGTH | awk -v BS=$BLOCKSIZE -v WD=$WORKDIR '{print "-SsL -r " sprintf("%d-%d", $0, $0 + BS - 1) " -o " sprintf("%s/%05d", WD, NR)}' | xargs -n 5 -P $PROCESS -I{} sh -c "curl {} $1"
-cat $WORKDIR/* > $OUTPUT
-rm -rf $WORKDIR
+[ -z ${OUTPUT} ] && { usage; echo "OUTPUT must be required" >&2; exit 2; }
+[ -z ${URL} ] && { usage; echo "URL must be required" >&2; exit 2; }
+
+WORK_DIR=`mktemp -d`
+atexit() {
+    rm -rf ${WORK_DIR} || true
+}
+trap 'rc=$?; trap - EXIT; atexit; exit $?' INT PIPE TERM
+trap atexit EXIT
+
+CONTENT_LENGTH=`wget --spider -S ${URL} 2>&1 | grep Content-Length | awk '$0=$2'`
+[ -z ${BLOCK_SIZE} ] && BLOCK_SIZE=$(( (${CONTENT_LENGTH} + ${PROCESS} - 1) / ${PROCESS} ))
+
+GEN_PARAM=`cat<<'EOF'
+{
+    block_path = sprintf("%s/%05d", WORK_DIR, NR);
+    printf("echo > %s", block_path);
+    printf(" && ");
+    printf("wget -q -c --header \"Range: bytes=%d-%d\" -O %s", $0, $0 + BLOCK_SIZE - 1, block_path)
+    printf("\n");
+}
+EOF`
+
+seq 0 ${BLOCK_SIZE} $((${CONTENT_LENGTH} - 1)) | awk -v BLOCK_SIZE=${BLOCK_SIZE} -v WORK_DIR=${WORK_DIR} "${GEN_PARAM}" | xargs -n 12 -P ${PROCESS} -I{} sh -c "{} ${URL}"
+
+rm -rf ${OUTPUT} || true
+for block in ${WORK_DIR}/*; do
+    dd if=${block} skip=1 iflag=skip_bytes bs=${BLOCK_SIZE} 2>/dev/null >> ${OUTPUT}
+done