To secure both of comfort at the ordinary seating attitude and comfort at the time of reclining backward movement of a seat back without complicating a structure.

A headrest support frame 14 energized and held in a backward tilting limit position by energizing force of an S spring 26 is interlockingly connected with a side frame 36 of a seat back frame as a reclining interlocking member through a wire cable 30, the interlocking region is prescribed and restricted as the reclining backward movement region of the seat back 16 in a predetermined angle or more by a delay interlocking means 34 provided on a connection end of the wire cable, an interlocking avoiding means 54 is provided on the connection end of the wire cable, and forward oscillation of the headrest support frame by receiving pressure of the load in the movement receiving part can be performed regardless of reclining movement of the seat back by the integral forward oscillation guarantee of the headrest support frame by the interlocking avoiding means.