Abstract: In a state where a shoulder member is in contact with a contact surface, a pin member is brought into contact with the contact surface to specify a pin movement amount, which is a distance from an initial position of the pin member to the contact surface, and specify a shoulder displacement amount, which is a displacement amount when the shoulder member is retreated as a result of the contact of the pin member. When both a first condition that the pin movement amount is included in a first range and a second condition that the shoulder displacement amount is included in a second range are satisfied, the pin member is retreated from the contact surface by a predetermined return amount, and furthermore, origin point alignment of the pin member and the shoulder member is performed on the basis of positions of the pin member and the shoulder member.