To provide an elevating device for a seat capable of performing elevating operation without enlarging an electric motor.

This elevating device 20 for the seat is composed of a swivel support mechanism 20A attached onto a vehicle body side and an elevating mechanism 20B for performing elevating operation while protruding the seat 15 out of a vehicle. The elevating mechanism 20B is provided with a four node link 43 connecting a seat 15 side and a swivel support mechanism 20A side mutually. When the four node link 43 is slid and operated for the vehicle body side, the four node link 43 turns to elevate the seat. Moreover, since the elevating mechanism 20B is provided with a compression coil spring 67 for energizing a base plate 37 constituting the four node link 43 in the direction of return, driving force of a motor 42 for advance and retraction required when the base plate returns is compensated by the compression coil spring 67 to miniaturize the motor 42.