To obtain a detecting apparatus which prevents the universal coupling of a motive-force transmission shaft being turned from being damaged due to an overload when the coupling is subjected to a turning motive force.

An apparatus is provided with a means 46 which is used to detect a twist generated at a motive-force transmission shaft 32 when the motive-force transmission shaft provided with one pair of universal couplings 34 at both end parts is subjected to a twisting force. The twist detecting means 46 is provided with two rotating member 48, 50 which are attached to both end parts of the motive-force transmission shaft or to parts near them and which can be turned together with the motive-force transmission shaft and with a detecting means. Both rotating members are provided with at least one set of opposite parts 64, 66 which are faced by keeping an interval around the motive-force transmission shaft. The detecting means is provided with a sensor 68 which is attached to one out of both opposite parts and which detects the approach of the other opposite part.