Kōsaku, Kosaku or Kousaku (written: 功作, 宏作, 幸作, 耕作, 耕筰, 興作, 孝作 or 浩作) is a masculine Japanese given name. Notable people with the name include:
, Japanese baseball player , Imperial Japanese Navy admiral , Japanese archaeologist and academic , Singapore-born Japanese businessman , Japanese footballer , Japanese karateka , Japanese sumo wrestler , Japanese golfer , Japanese poet and writer , Japanese composer and conductor , Japanese film director , Japanese physician and translator , Japanese mathematician