PURPOSE: To make it possible to inspect the state of a minute through hole without reqiring a special technique and with efficiency by providing a pressure storage chamber at the outside of the through hole, forcing air via the through hole and deciding good or bad in a period of time in which air reaches a specific pressure.

CONSTITUTION: To the receiving plate 2 of a fixed bedplate 1 there is fitted a round bar-like main body 3. A cylinder 4 is fitted in the main body and pressed and fixed by means of a clamp 37. Then, a through hole 7 is worked into a specific dimension by a drill 1a, and the pressure storage chamber is closed by a packing 38 and a lid 45, and a pressure detector 40 is connected thereto through a hole 38a. In this state, pressure air is caused to flow into the detector 40, where the air pressure is measured. Upon this occasion, even if the hole 7 is worked correctly, if there is no pressure storage chamber, the time for sensing the air pressure is short but the hole comes to have a specific pressure after a specific period of time, and thereafter the judgement of good or bad of the through hole can be carried out very easily.