A fuel cell stack includes an insulating collar member provided in an end plate and screwed with a positioning pin, and a rotation restriction mechanism that restricts rotation of the collar member relative to the end plate in a screw tightening direction of the positioning pin. A method of assembling the fuel cell stack includes a screwing step and a stacking step. In the screwing step, rotation of the collar member relative to the end plate in the screw tightening direction of the positioning pin is restricted by the rotation restriction mechanism.