PURPOSE: To enable the prevention of the forward shift of a buttock part via a support in a case such as collision by providing a downward projected bead on a plate spring with the rear end thereof fitted to a frame front, and a downward projected stopper flange at both sides of a panel, and covering an entire top surface with a cushion pad.

CONSTITUTION: When a passenger is seated on a reference position, his/her buttock part causes an S-type spring 2 and a cushion pad 7 to be flexible, thereby generating comfortable cushion quality. At the forward part of a seat, his/her thigh is supported with a plate spring 5 and the cushion pad 7. When the plate spring 3 is subjected to a load from the buttock part and a bead 4 comes so flexible as to be in contact with a frame 1, the reaction force of the plate spring 3 comes forward of the bead 4 and it becomes possible to support the thigh on rather hard cushion matching the hardness of the buttock part. At the time of collision, the forward shift of the buttock part generates a high load on the forward part of the seat, and a panel 5 becomes flexible so downward as to cause the contact of a stopper flange 6 with the frame 1. In addition, even when the flange 6 comes in contact with the frame 1, no further sinking occurs due to the front rise of the panel 5 and the further forward shift of the buttock part can be prevented.