To compactly house a machine body at folding-up/housing time while increasing stability by dislocating a gravity center position of the machine body backward by expanding a distance between a competition court and a base stand at machine body using time and projecting a balance weight outward to the rear of the base stand, by respectively arranging a movable balance weight in an extensible/contractible lifting frame having a backboard and the base stand.

While a sliding frame 5 is slidingly fitted to a lifting frame 4 having the base end pivotally fixed to main/sub-supports 2, 3 on a base stand 1, connecting levers 21, 22 arranged in the base stand 1 are connected to a main support receiving metal fitting, and while lifting operation of the lifting frame 4 is performed through operation of these interlocking levers 21, 22, interlocking operation of a balance weight 18 and the interlocking levers 21, 22, rotary operation, manual operation by removing the interlocking levers 21, 22 and also horizontal rotation can be performed.