PURPOSE: To improve the assembling workability, and make a thickness of each member thin by combining multiple frame members in the predetermined state.

CONSTITUTION: A hook projecting part 12 enters into a hook hole 21 and the hook end surface of the projecting part 12 is hooked on a hole edge of the insertion hole 21 with the overlap of bent pieces 7, 10 and a vertical piece 15 in the horizontal direction. Each end of frame materials 2, 3 are connected to each other, and simultaneously, both ends of both the frame materials are overlapped with each other in the vertical direction, and a standing piece 18 is fitted in the end of a horizontal piece 4 to pinch the end of the horizontal piece 4 from the upper and the lower between the horizontal piece 4 and the standing piece 18, and the distortion of a fitting frame is restricted. Hook projecting parts 22, 13 enter hook holes 30, 33 with the overlap of a vertical piece 5 with an intermediate bent piece 33 of a socket fitting fixture 25 and the overlap of a vertical piece 15 with an end bent piece 28 of the socket fitting fixture 25 in the horizontal direction, and the hook surface of each projecting part is hooked on a hole edge thereof. The fitting fixture 25 is thereby connected to the fitting frame. Simultaneously, a horizontal piece 27 of the fitting fixture 25 is overlapped with the lower surface of the ends of the horizontal pieces 4, 14 overlapped in the vertical direction.