PURPOSE: To position automatically a cable inserted into a pipe, by providing a position measurer different in length from a guider and discriminating the difference of length by a non-contacting detector.

CONSTITUTION: A charging device 13 is moved to a heat transmission pipe 18 to be examined, and a cable 12 with an ultrasonic probe 10 is inserted into the pipe 18. A position measure 60 different in length from a guider 11 is provided between the probe 10 and the guider 11. The rotation number of a drum 16 around which the calbe 12 is wound up is detected by an encoder 27 for the purpose of detecting the position of the inserted probe 10, and this rotation number and a count signal obtained by counting the number of guiders 11 by a photodetector 24 connected to light emitters 61A and 61B and photodetectors 62A and 62B are inputted to a position measuring device 31 and are processed to detect an accurate position. Lengths of the probe 10 and guiders 11 are made longer than intervals of two pairs of light emitters 61A and 61B and photodetectors 62A and 62B, and the length of the measurer 60 is made shorter than those, and thus, signals from the measurer is distinguished from signals from the probe and guiders because signals from the measurer do not overlap.