To easily measure the inner diameter of a measured hole in a various kinds of works while reducing time required for making preparation of changing kinds of the works.

An instrument mounting holder 24 for receiving a measuring instrument 27 can lift up and down in response to the lifting of a lifting base 15, tilt according to tilting of a tilting table 19, and slide transversely in relation to a movable support block 22. A first spacer 16 is selectively interposed between a support frame 14 and the lifting base 15, a second spacer 20 is selectively interposed between the tilting table 19 and the lifting base 15, and a third spacer is selectively interposed between the movable support block 22 supported by the tilting table 19 and the measuring instrument mounting block 24. A lifting position of the lifting base 15, a tilting angle of the tilting table 19, and a transverse position of the instrument mounting block 24 corresponding to each selected spacer are fixed by a lifting position fixing means 21, a tilting angle fixing means, and a transverse position fixing means.