A method for joining members according to an embodiment of the present invention includes: providing a bumper stay including two integrated pipe portions extending in an identical direction, the bumper stay including a recess provided between the pipe portions being adjacent to each other, the recess extending in a longitudinal direction of the pipe portions from end surfaces of the pipe portions, a part of the recess serving as a locking portion, and a bumper beam including a rear inclined wall formed with two hole portions into which the pipe portions of the bumper stay are insertable respectively; inserting the bumper stay into the hole portions of the bumper beam until the locking portion abuts on the rear inclined wall; and pipe-expanding an insertion portion of the bumper stay into the bumper beam to join the insertion portion to the bumper beam by press-fitting.