To provide a seat which can optionally adjust the tension of a seat member.

This seat is provided with a tension regulating means 40 for regulating the tension of the seat member stretched over a seat frame 20. The means 40 is provided with a regulating member 41, a locking member 42, engaging members 23b, 42d and an elastic member 43. The regulating member 41 is formed to be able to wind and rewind the seat member 11. The locking member 42 is connected in a power transmittable and axially movable manner to the regulating member 41. The engaging members 23b, 42d are provided between the locking member 42 and a frame member 20 so as to be engaged and released from engagement by the axial movement of the locking member 42. The elastic member 43 energizes the locking member 42 in the engaging direction of the engaging means.