A casting die of the present invention includes a stationary die, a movable die, and a sliding die provided to the movable die so as to be insertable and withdrawable in a direction crossing a movement direction of the movable die and configured to form a cavity in collaboration with the stationary die and the movable die. The sliding die includes a slider core that is moved so as to be insertable and withdrawable along the movement direction of the movable die and a stopper that is in contact with the slider core at a die closing position and locks the slider core.