PURPOSE: To sufficiently secure a space for placing baggages and feet, facilitate cleaning of the underneath of a seat cushion of seat main body, and prevent electric wiring for heater member from being largely exposed, even when the heater member is installed under the seat main body.

CONSTITUTION: A base frame 3 is cantilever-likely supported on a leg part fixed onto a cabin floor surface, and a seat main body is supported on the base frame 3. A pair of front and rear heater members 10 are fitted along front and rear outside parts 3a in the longitudinal direction of the base frame 3. Or, a nearly U-shape heater member 10 is fitted along the outside part of the base frame 3.