Vehicular seat including forward movable headrest

A vehicular seat having a forward movable headrest, comprising:

• a main frame which is provided to a seat back which supports a back of an occupant who sits in the back seat, the main frame including an upper frame which is positioned at an upper part of the seat back and extends in a widthwise direction of the seat back, and a pair of side frames which extend downward from both ends of the upper frame;
• a headrest support frame which is arranged at an upper part of the main frame and can move from a first position in the vicinity of the upper frame to a second position close to the occupant, the headrest support frame having an upper portion which is arranged in substantially parallel with the upper frame on a front side of the upper frame;
• a headrest which is attached to the headrest support frame and opposed to a head of the occupant;
• an actuator unit comprising:
• a piston which moves in a direction along the upper frame;
• a cam member which can enter a gap between the upper frame and the upper portion of the headrest support frame;
• a transmission mechanism which transmits movement of the piston to the cam member, and thrusts the headrest support frame toward the second position by causing the cam member to enter the gap between the upper frame and the upper portion of the headrest support frame;
• and
• a stopper which is provided to the main frame and receives the headrest support frame when the headrest support frame moves to the second position,
• wherein the actuator unit which is attached along the upper frame, generates a drive force when an impulse force equal to or above a predetermined value is applied to a vehicle, and moves the headrest support frame in a direction along which it approaches the occupant by transmitting the drive force to the headrest support frame.