A headrest: configured to be adjustable in the forward-backward direction and comprising support mechanisms (5, 6) for supporting a second member (4) with respect to a first member (3) in a state in which the second member can move forward and backward, a backward movement-regulating member (7) for allowing forward movement of the second member (4) at each use position while regulating backward movement, and a backward movement regulation-releasing member (8) for moving the backward movement-regulating member (7) to the backward movement regulation-releasing side when the main headrest body (1) is moved to a forward area outside of the range of use that is further forward than the forwardmost use position; and configured so as to also comprise a forward movement-regulating member (9) for regulating the forward movement of the second member (4) by coming into contact with the first member (3) when the main headrest body (1) is moved forward and reaches the forwardmost use position and an operation means (10) for moving the forward movement-regulating member (9) to the forward movement regulation-releasing side.