To improve supporting performance of a side support and to effectively utilize the inside thereof.

The side support 20 of a vehicle seat 2, constituted by a flexible plate-shaped member and bent to be detachably attached to a seat frame 10 on a side of the vehicle seat 2, includes: a first attaching part 24 for attaching one end of the side support 20 to the front side of the seat frame 10; a hinge part 26 capable of bending the side support 20 on the way after swelling one end of the side support 2 relative to the seated face (composed of a net body 60); and a second attaching part 28 for attaching the other end of the side support 2, different from the one end, to the rear side of the seat frame 10, different from the front side.