--- Net::FTP#retrbinary(cmd, blocksize, rest_offset = nil, callback = Proc.new)

    Сcmdǻꤵ줿ޥɤꡢХʥǡ 󤻤ޤ
    blocksizeǻꤵ줿Хñ̤ǥǡ
    ɤ߹ߡcallbackǻꤵ줿Proc֥Ȥޤ
    ֥åɤ߹ǡϤޤ

