A reciprocating mechanism includes a worm shaft with a helical groove and a sliding member. The worm shaft is disposed parallel to a spool shaft. The sliding member moves back-and-forth along an axial direction of the spool shaft by rotation of the worm shaft. The sliding member includes a body member with a recess portion having an engaging member. The engaging member includes an engaging portion, a first shaft portion and a second shaft portion. The engaging portion engages with the helical groove. The first shaft portion is formed on an end portion adjacent the engaging portion to have a diameter smaller than a diameter of the engaging portion. The second shaft portion is formed on an end portion of the first shaft portion that is remote from the engaging portion 70 to have a diameter smaller than a diameter of the first shaft portion.