To provide a chair using a gas cylinder as a leg support, capable of being nested, and improved in reliability in strength and flexibility in design of members such as a backrest.

A fixing base 8 is fixed on the upper end of a leg support 4, and right and left support frames 9 are set on the fixing base 8 in an upwardly-projecting manner. A seat 2 is fitted on a movable base, and the movable base is connected to the support flames 9 at a position near the rear end of the seat 2 and higher than the fixing base 8. The weight of the seat 2 in use is supported by the fixing base 8 at the lower projection rim 29 of the front end part of the fixing base 8. A backrest 3 can be designed without being restricted by the seat 2 because the seat 2 can be flipped up to face the backrest 3. The chair is excellent in supporting strength and stability because the weight in use is supported by the front end part of the fixing base 8.