PURPOSE: To enable inspection of a heat-transfer tube on remote operation, by inserting a flexible cable having a sensor at the tip thereof into a heat- transfer tube in a heat exchanger to be moved to a desired position in such a manner as to rotate and move vertically.

CONSTITUTION: Heat-transfer tubes 14 are in a heat exchanger body 1. A flexible cable 3 having a sensor 30 at the tip is advanced and retracted within the heat transfer tube 14 to inspect it. A guide pipe is inserted into an inspection hole provided at the top of the body 1 and a means is provided to make the guide pipe rotatable and vertically movable. Parallel links 41 and 42 are mounted at the lower end of the guide pipe and the flexible cable 3 is made mobile and moved to a desired position by the operation of the links 41 and 42 to be inserted into each of the heat-transfer tubes 14. This permits the insertion of the sensor 30 at the tip of the flexible cable 3 into the heat-transfer tube 14 at a desired position to eliminate the need for opening the body, thereby facilitating the inspection of a number of heat-transfer tubes on remote operation.