To achieve compact roll-in in a chair which rolls in the front part of a seat downward and deforms it.

The front part of a seat inner shell 8 is a deformation allowed part having many front slits. A seat outer shell 7 is separately constituted of a fixed outer shell and a sliding outer shell 11, and the front part 8d of the seat inner shell 8 is rolled in downward interlocked with the retracting movement of the slide outer shell 11. At the front part of a cushion 9, a deformation allowed part 9b having a column of groove lines 33 is formed. Projections 34 between the groove lines 33 are mounted on the support bar part 29 of the seat inner shell 8. Thus, biting between the deformation allowed part 9b of the cushion 9 and the deformation allowed part 8a of the seat inner shell 8 does not occur, and the front part of the seat 4 can be smoothly rolled in compact.