To reduce the number of parts and working man-hour in a rising assistant mechanism for assisting rising of a seat lifter by providing a torsion bar 50 in a hollow pin 10.

In the rising assistant mechanism of the seat lifter, turning of a lift member turnably supported on a base through the hollow pin 10, turnably connected to the seat support member and supporting the seat support member is assisted by counter twisting force of a torsion bar 50 generated by twisting a projection end 55 projected from an opening 15 of the hollow pin 10 and engaging its distal end with the base. First and second engagement wall parts 11, 12 are projectedly at opposed positions on an inner peripheral surface of the hollow pin 10, a first bent apex part 511 of a bent part of the torsion bar 50 is engaged with the first engagement wall part 11 and the second bent apex part 512 is engaged with the second engagement wall part 12.