Torque measuring device assuring timely maintenance work

A torque measuring device for a rotating body comprises: a rotary section composed of first and second flanges to be joined respectively to a driving shaft and a driven shaft, and a hollow cylinder having the first and second flanges formed respectively on both edges thereof; light emitting elements provided at an outer circumference of the rotary section and adapted to emit light according to an output from torque detectors provided at an inner circumference of the cylinder thereby generating an optical signal; a light receiving fiber to receive the optical signal from the light emitting elements; optical-electrical signal converters provided so as to face both end surfaces of the light receiving fiber, and adapted to convert the optical signal into an electrical signal; and a malfunction detector to detect malfunction of the light receiving fiber according to the electrical signal from the optical-electrical signal converter.