To prevent the height of a table set in a horizontal position from being changed even if a seat back is vertically moved.

This structure has a seat body 3 comprising a seat bottom 31 and a seat back 34, and a table 6 provided on the back of the seat back 34. The height of the seat back 34 is adjustable. The structure is provided with a second bracket 42 provided on the rear end of a frame 2 and protruding backward and having a second horizontal shaft 54 extending in the direction of width, and a table support arm 51 rotatably supported by the second horizontal shaft 54 such that the position can be changed between an erect position of abutting on the back of the seat back 34 and a reclining position of separating from the back of the seat back 34 and having a third horizontal shaft 61 extending in the direction of width at the top thereof. The table 6 is rotatably supported by the third horizontal shaft 61 such that the position can be changed between an erect position and a horizontal position and is set always at the same height in the horizontal position irrespective of the height of the seat back 34.