PURPOSE: To obtain a working stage device which can be provided in a pressure chamber so as to execute work for fitting or removing a body to be tested or external observation and enables regulation of an effective depth width of a working stage in accordance with the thickness of the body to be tested and which is excellent in operability and safety.

CONSTITUTION: A plurality of longitudinal rods 12 which are provided vertically at prescribed intervals in the lateral direction and also can be moved in the depth direction and fixed at prescribed positions are provided in a pressure chamber C, and a main working stage 14 is fixed horizontally on the inner wall 5 of the pressure chamber with spaces 13 for movement of the longitudinal rods left, while one end part in the width direction of a rotary working stage 16 is fitted rotatably between the adjacent longitudinal rods and at a position being higher a little than the upper surface 15 of the main working stage. The rotary working stage is so designed that it can be made vertical substantially and held in a state of being rotated upward and can be made horizontal substantially and provided continously to the upper surface of the main working stage in a state of being rotated backward.