PURPOSE: To obtain a device which can hold the thin film type optical element in one plane with extremely high precision by generating a fluid force which holds the thin film type optical element at a fixed position by relative movement caused by a moving means between the thin film optical and a positioning element.

CONSTITUTION: When a couple of fixed bodies 200 and 300 having slanting surfaces 201 and 301 are positioning above and below a moving surface 100, only one place where a force P2' generated by the moving surface 301 and slanting surface 201 and force P3' generated by the moving surface 100 and slanting surface 301 become equal to each other is generated. When the moving surface 100 approaches the slanting surface 201, the P2' increases and the P2' decreases, but when the moving surface 100 approaches the slanting surface 301, the P3' increases and the P2' decreases, on the other hand. Thus the moving surface 100 is held at one point (one plane) between the slanting surface 201 and slanting surface 301 with the fluid force. Here, h2 and h3 need not be equal to each other and the gradients of the slanting surfaces 202 and 301 need not be equal either.