To accommodate a side cabinet in the lower space of the top plate of a desk when the surface of its top plate is not used and widen the surface of the top plate of the side cabinet so as to be flush with the top plate of the desk and easily perform a work when the surface of the top plate is not used.

A desk 1 and a side cabinet 7 are provided. A space 5 is provided below the top plate 2 of the desk 1. The side cabinet 7 comprises a main body 8, a top plate 9 provided on the upper part of the main body 8 so as to be freely lifted, a top plate flap 10 provided at the back of the top plate 9 so as to be collapsible to a substantially horizontal state and to a suspended state and holding means for holding the substantially horizontal state of the top plate flap 10. The length of the main body 8 and the top plate 9 in the side cabinet 7 is shorter than the length of the space 5 provided below the top plate 2 of the desk. When the top plate flap 10 is lifted in the substantially horizontal state, the length from its rear end 10a to the front end of the top plate 9 is substantially the same as the length in the transverse direction of the top plate 2 of the desk.