PURPOSE: To make a large material held between a receiving part and a pressing part easily rotatable and invertible by installing the receiving part, free of rotation, in an arm tip on one side, out of two arms being opposed to each other, and also installing the pressing part in an arm tip on the other free of slide motion and rotation.

CONSTITUTION: When polishing work for one or plural surfaces, where a large material M is workable, is over, a hydraulic cylinder 28 is operated for its extension and this large material M is held between a pressure receiving plate 13 and a pressure plate 23. Next, another hydraulic cylinder 9 is operated for its extension, uprighting a pair of arms 4, 5, and the large material M is lifted up to such a height where work is easy to be done and there is no hindrance for inversion or rotation, whereby this material is rotated as far as 180 degrees by manual operation of an operator. Afterward, the hydraulic cylinder 9 is operated for its contraction and the large material M is lowered on a frame 1. Then, the hydraulic cylinder 28 is operated for its contraction, releasing the holding of the large material M, and these paired arms 4, 5 are set to the most upside-down-position. In this state, the next surface of the large material M is polished.