Headrest for an automobile seat

A seat apparatus comprises: a seat back provided with a seat back frame; a head rest frame supported to the seat back frame via a tilting shaft so as to be freely tilted in forward and rearward directions; a head rest supported to an upper side of the tilting shaft in the head rest frame; a gas actuator mounted to the seat back frame, operated due to a momentary gas generation and tilting the head rest frame in a direction in which the head rest is tilted forward at a time of the operation; and an acceleration sensor for detecting an acceleration of the automobile in the forward and rearward directions. The gas actuator is operated when the acceleration sensor detects a predetermined or greater acceleration.