To provide a stackable chair having excellent quality in design, use, handling, cost, function or the like.

The chair comprises a frame main body 10 which has a pair of side frames 3 including front legs 1 and rear legs 2, which are connecting to each other, and which has a lateral frame 4 for connecting the side frames 3, a back seat 20 axially supported to edge sections of arm rest sections 5 that are formed extending the front legs 1, and a seat 30 axially supported to the lateral frame 4. The back seat 20 is axially supported to the edge sections of the arm rest sections 5 on adjacent middle sections thereof, and has a locking mechanism. A locking means includes hinge brackets 11 slidably engaged to an upper edge of the arm rest sections 5, and springs for pressing the hinge brackets 11 to the side of the arm rest sections 5 to realize easy housing and excellent function.