The purpose of the present invention is to provide a novel antitumor agent that exhibits a remarkably excellent antitumor effect and has few side effects. The present invention relates to an antitumor agent characterized by the concomitant administration of an acyl thiourea compound represented by general formula (I) or a salt thereof and an immune checkpoint regulator.本發明的目的在於提供一種新穎的抗腫瘤劑，其顯示出顯著優異的抗腫瘤效果，且副作用少。本發明是關於一種抗腫瘤劑，其特徵在於：合併投予由通式（I）表示的醯基硫脲化合物或其鹽、與免疫檢查點分子調節劑。
