A seat cushion of a vehicle seat has a base seat whose front end is anchored to a front frame of a frame for a sitting portion, and whose rear end is connected to a rear frame of the frame for a sitting portion via helical tension springs. A supporter, supported via helical tension springs at a pair of left and right side frames of the frame for a sitting portion, is disposed at a lower side of the base seat so as to support a femoral region of a seated person. The supporter and the helical tension springs structure an auxiliary vibration system whose mass element is a femoral region of a seated person. The auxiliary vibration system is made to function as a dynamic vibration absorber with respect to up-down vibrations of a main vibration system whose mass element is an upper body of a seated person.