PURPOSE: To reduce the man hours for plural setup changes of a machined hole inspection for the different kind of a work at a low cost.

CONSTITUTION: One end of a probe 1 is energized and inserted loosely so as to be projected by a prescribed length into a probe holder 2 in which single displacement detectors 7, 8 installed on a sliding shaft 4 are provided and one plate 9 selected from plural setup change plates is mounted/dismounted so as to be changed freely to/from the mounting groove of the probe holder 2. When the insertion upto a regulated depth of even one probe among plural probes is obstructed by the lack of the machined hole of a work or the shortage of the depth, the movement of the probe holder is obstructed by the hit of the other end of the probe to the setup change plate 9 and the displacement of the sliding shaft, on which the probe holder is installed, is detected by a displacement detector and the mis-machining is indicated.