PURPOSE: To improve comfort by providing an opening having a front end and a rear end in the center of a seat frame, arranging a plurality of horizontal springs between the front end and the rear end of the opening in such a way that they converge toward the front end and placing a seat pad of elastic material over the springs.

CONSTITUTION: A large opening 14a is provided in the center of a frame 14 of engineering plastic such as polypropylene and having a large part 11b and a narrow end part 11a. A plurality of horizontal coil springs 17 are arranged in the opening 14a in such a way that they converge from the large part 11b toward the narrow part 11a. Then the springs 17 are disposed for uniformly covering the opening 14a. A cloth covering 19 is placed on the upper surface of the frame 14 and an elastic pad 21 of polyurethane foam rubber or the like is placed on the sides of the frame 14 in such a way that an upper part of the seat is formed.