To provide a chair improved in handleability by bringing the back part of a top plate closer to the side of a user in a back seat in the horizontal state of the top plate even in the case of arrangement of a front seat and the back seat set at a large internal and easy to perform the tilting operation of a backrest and easy to hold the horizontal state of the top plate.

The upper end of a link connection rod 7 is pivotally attached to the intermediate part of the side part of a back plate 11 and the lower end of the link connection rod 7 is disposed to a sliding shaft 8 freely slidably and turnably engaged with a vertical groove 6 provided on the side face of the back part of a frame main body 5. Then, a releasable locking piece pivotally attached to the side face of the frame main body 5 at the upper side part of the groove part 6 for passing through the sliding shaft 8 of the link connection rod 7 toward an upper part inside the groove part 6 but blocking return to a lower part is provided and the backrest is held in a horizontal state.