To provide a foldable chair, which is folded with a simple operation and has enough strength to be seated by a person.

A chair is composed of two standing boards 1, having shape of rectangles and placed in tandem, and bendable seating parts 2 that are installed to the top and bottom parts of the both boards 1, and bellows 3 that connect the left and right parts of the both standing boards 1. Protruding pieces, which vertically move inside the bellows 3, are protruded parallel to the standing boards 1 at the center part of the top and the bottom seating parts 2. When the standing boards 1 are so pushed to shorten the space between the boards that the bellows shrink, the seating parts 2 are protruded from the top and the bottom, the protruding pieces move in separating directions and the chair is folded. When seating parts 2 of the folded chair are pushed from the top and the bottom, they impinge against the top and the bottom edges of the bellows 3, so that the seating parts 2 becomes horizontal. The end tips of the protruding pieces are brought into contact with each other to hold the seating parts 2.