To reduce a storage space of chairs when they are folded and stuck and reduce the weight of a chair while retaining the strength.

In a foldable chair 1 that has a tubular front leg frame 2 and a tubular rear leg frame 3, a seat 4, hinges 5 rotatably connecting the frames 2 and 3 and the seat 4 and can be folded by rotating the frames 2 and 3 and the seat 4 by the hinge 5, the parts of the frames 2 and 3 in which the hinges 5 are provided are double tubular structures, parts other than those are single tubular structures and are slenderized to the extent of having minimum stiffness against a load.