def _download(file_name):
    file_path = dataset_dir + "/" + file_name

    if os.path.exists(file_path):
        return

    print("Downloading " + file_name + " ... ")
    # urllib.request.urlretrieve(url_base + file_name, file_path)  #←この行をコメントアウト
    
    # ↓↓↓　追加　↓↓↓

    headers = {
        "User-Agent": "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:47.0) Gecko/20100101 Firefox/47.0"
        }
    request = urllib.request.Request(url_base+file_name, headers=headers)
    response = urllib.request.urlopen(request).read()
    with open(file_path, mode='wb') as f:
        f.write(response)
    # ↑↑↑　追加　↑↑↑
    
    print("Done")