An actuator device for a rider-posture changing apparatus of a human-powered vehicle comprises a cam follower and a cam member. The cam member is rotatable about a rotational axis. At least one of the cam follower and the cam member includes a curved surface contactable with another of the cam follower and the cam member to move the cam follower in a movement direction in response to a rotation of the cam member. The movement direction is different from a circumferential direction defined about the rotational axis. The curved surface has a curved shape in a first cross-section perpendicular to the circumferential direction.