Patent ID: 7770967

Claim:
A head rest device comprising: a head rest rear portion configured to be supported to a seat back; a head rest front portion freely moving forward and backward between a fully-closed position coming close to the head rest rear portion and a fully-open position separated from the head rest rear portion; a driving device moving the head rest front portion; a control circuit controlling the driving device so as to move the head rest front portion; a sensor electrode structured such that a capacitance is changed in accordance as a head of an occupant approaches the sensor electrode; and a capacitance detecting circuit detecting the approach of the head of the occupant on the basis of a change in the capacitance of the sensor electrode, wherein the sensor electrode is mounted to the head rest front portion, wherein the driving device, the control circuit, and the capacitance detecting circuit are mounted together to one of the head rest front portion and the head rest rear portion such that when the head rest front portion is moved between the fully-closed position and the fully-opened position, a distance changes between the driving device, control circuit, and capacitance detecting circuit mounted on one of the head rest portions and the other head rest portion.