A step device for a vehicle includes: a movable step supported under a door opening; a coupling member that moves the movable step in a vehicle width direction in conjunction with opening and closing of a sliding door; and a sub-step that is disposed under the door opening. The movable step moves under the sub-step toward an outer side in the vehicle width direction so as to be disposed in a deployed position in which the movable step protrudes from the sub-step toward the outer side in the vehicle width direction. The sub-step has an overlapping region that covers an upper side of the movable step in a state where the movable step is disposed in the deployed position.