A step device for a vehicle including a movable step arranged in a doorway opened and closed by a door is disclosed. The step device includes a drive unit, an open/close mechanism, a projection/retraction mechanism, and a plate cam. The open/close mechanism opens or closes the slide door. The projection/retraction mechanism moves a movable step. The plate cam is rotated by the open/close mechanism and engaged with a bushing arranged on the projection/retraction mechanism to enable or disable power transmission between the open/close mechanism and the projection/retraction mechanism. The plate cam includes a first recess and a second recess. The first recess pushes the bushing during rotation of the plate cam when the slide door is in a range of a predetermined open/close position to enable or disable power transmission between the open/close mechanism and the projection/retraction mechanism. The second recess frees the bushing from the pushing during rotation of the plate cam and disables power transmission between the open/close mechanism and the projection/retraction mechanism when the slide door is outside the range of the predetermined open/close position.