The present invention aims at providing an automobile headrest which can be prevented from being drawn out inadvertently or on purpose, can be drawn out through a special operation if necessary, and includes a falloff preventing device allowing the same components as those of a height adjusting mechanism to be used. In an automobile headrest in which a headrest stay for supporting the headrest is vertically adjustably inserted and supported in a headrest bush, a headrest falloff preventing device including a locking mechanism for preventing the headrest from falling off and an unlocking mechanism for unlocking the headrest is attached to the headrest bush at a position inside a seat back. A falloff preventing notch is formed in the headrest stay. A lock member that abuts on the inserted headrest stay due to a resilient force of a spring is provided to the headrest bush so as to free to reciprocate. The headrest falloff preventing device is provided with the locking mechanism for preventing the headrest from falling off through engagement of the lock member with the falloff preventing notch of the headrest stay and the unlocking mechanism for disengaging the lock member from the falloff preventing notch through an operation of the lock member against the resilient force of the spring.