A window regulator 1 comprising a main arm 10 as an arm member having one end thereof in the longitudinal direction rotatably coupled to a drive unit and the other end thereof movably coupled to a window glass. The main arm 10 has: an inside extension section 11 extending in a stepped manner via first and second inside bending sections 111, 112; and an outside bead section 12 that bends and protrudes from an outer peripheral end of the inside extension section 11 to the outside and is bent in a step shape, via the first and second outside bending sections 121, 122. The first and second inside bending sections 111, 112 are formed between the first outside bending section 121 and the second outside bending section 122.