To increase the strength of the entire leg frame without thickening a pipe material or using a strong pipe material and to provide a light-weight and inexpensive chair.

The chair 1 is composed by attaching a seat 4 and a backrest 3 to a pair of left and right support frames 8 in the leg frame 2. The leg frame 2 is composed of a base frame 6, which is opened at the front and U-shaped in the plane view and the pair of left, and right support frames 8, which is erected from the left and right front ends through corner frames 7 in an arc shape. The cross section of the pair of left and right support frames 8 is made circular, the horizontal section of the left and right corner frames 7 is made into an elliptic shape whose anteroposterior dimension is larger than the longitudinal direction, and the vertical section of a side frame 6a in the base frame 6 is made into the elliptic shape whose vertical dimension is larger than the longitudinal direction.