A vehicle seat comprising a pair of side frames configuring a portion of a seatback frame serving as framework for a seatback; a deformation origin portion provided to at least one of the pair of side frames and acting as an origin when the side frame deforms due to a collision force imparted to the seatback frame during a rear-on collision; and a deformation suppression unit provided to the side frame provided with the deformation origin portion, permitting deformation of the side frame originating at the deformation origin portion and suppressing deformation of the side frame by a reference amount or greater by the deformation suppression unit making contact with a contacted member provided to the seatback frame when the deformation amount of the side frame has reached the reference amount.