PURPOSE: To secure sufficient space between a seat and a seat setting surface at the lower side of the seat, and to improve the anti-abrasion property of the installing part of a gas lock mechanism as a reclining mechanism, as well as to allow to operate to convert the directions of a seat back and a seat cushion in a necessary condition.

CONSTITUTION: A base frame 22 is held in a cantilever form to a leg 21 fixed on the floor surface in a car room, and a seat main body 20 is held rotation regulatable to the base frame 22 through a rotation regulating mechanism 23. A reclining mechanism is formed of a gas lock mechanism 26 having a gas cylinder and a piston rod. A metallic collar 37 is fitted to a holding shaft 31 projected at the seat cushion frame 25 side. A bracket at one side of the gas lock mechanism 26 is pivoted to the collar 37.