Abstract: A unit for testing infrared radiation detection units which incorporate relay contacts that are readily rendered defective by increasing resistance through use, thereby rendering the infrared radiation detection unit defective or inaccurate. As an example, such radiation detection units which are tested include hot metal detectors, loop controllers or scanners, and optical barrier units used in steel manufacturing. The testing unit includes an infrared radiation source for radiating infrared rays to an infrared radiation detector on a detection unit to be tested, and the testing unit further includes a relay contact resistance tester for measuring resistance of the relay contacts which is comprised of a plurality of light emitting diode indicators connected in parallel with each other through a resistor current divider network which is connected in series with a power source and the relay contact in the unit to be tested.