To provide a board supporting device in which any wasteful space can be excluded from between a circuit board and a board supporting wall.

A board supporting device is provided with a board supporting wall 31 having an upper face 31a, lower face 31b positioned at the opposite side to this upper face 31a, and through hole 42 opened on those upper face and lower face, circuit board 35 arranged along the upper face of the board supporting wall 31, screw 63 for fixing the circuit board 35 to the board supporting wall 31, and metallic screw bearing 50 supported by the board supporting wall 31 and faced to the through hole 42. The screw bearing 50 is provided with a recessed part 51 for housing a screw head 63a. The recessed part 51 is recessed so as to be inserted from the direction of the lower face of the board supporting wall 31 into the through hole 42, and this is provided with a bottom board 52 continued to the upper face of the board supporting wall 31, and a screwing hole 61 into which the screw is screwed is opened in this button board 52.