A head rest rear portion is supported to a seat back. A head rest front portion is movable forward and backward between a full-close position that is brought into contact with or close to the head rest rear portion and a full-open position that is a predetermined distance away from the head rest rear portion. A drive mechanism moves the head rest front portion. A detection sensor provided in the head rest front portion includes an electrode having a head portion detecting antenna electrode for detecting a head portion of an occupant at a time when the head rest front portion moves in the full-open position direction, and a finger detecting antenna electrode for detecting a finger of the occupant in a rear seat or the like at a time when the head rest front portion moves in the full-close position direction.