The laser apparatus includes a laser oscillation part including a water-cooled plate, an air cooling machine including a radiator, a dehumidifier including a water-cooled plate, and a cooling water supply device including a cooling water pipe through which a cooling water is supplied. The air cooling machine and the dehumidifier are arranged in a housing. The cooling water pipe is branched so that the water-cooled plate in the laser oscillation part, the radiator, and the water-cooled plate in the dehumidifier are connected in parallel. The cooling water supply device supplies a common cooling water of the same temperature to the water-cooled plate in the laser oscillation part, the radiator, and the water-cooled plate in the dehumidifier.