RECIPROCAL MOVEMENT DEVICE

A forward/backward movement device includes: a case; a guide member that is housed in the case and includes a shaft and a protrusion formed on an outer peripheral surface of the shaft; and a forward/backward movement member having a cylindrical shape. The forward/backward movement member includes a groove that is formed on an inner peripheral surface of the forward/backward movement member and moves forward and backward with respect to the case while rotating by being guided by the protrusion. The groove is a portion where the protrusion slides. Thereby the forward/backward movement device can be miniaturized while preventing the intrusion of water.