According to this invention, there are provided a stopper stopping forward pivoting of a seat back at the position of a forwardly tilted state, a stopper operation mechanism, a reclining mechanism switching the seat back between a free state in which it can be pivoted with respect to a seat cushion and a lock state in which it cannot be pivoted with respect thereto, a reclining lever, and a connection lever. Through operation of operation levers the seat back is placed in the free state via the stopper operation mechanism, the connection lever, and the reclining lever, and the stopper is moved via the stopper operation mechanism. And, between the stopper operation mechanism and the reclining lever is provided a retention mechanism that retains the stopper at a position to which the stopper is moved.