A method of attaching a wafer by suction, includes a step of mounting a wafer on a right arm and a left arm of a transfer jig, moving the transfer jig toward a wafer suction stage in such a manner that a facing right arm surface of the right arm slides along and in contact with a first side surface of the wafer suction stage and a facing left arm surface of the left arm slides along and in contact with a second side surface of the wafer suction stage until the wafer comes to lie directly above a mounting surface of the wafer suction stage, mounting the wafer on the mounting surface by moving the transfer jig downward toward the wafer suction stage while maintaining the contacts, and attaching the wafer to the mounting surface by suction.