To provide a degradation diagnostic device of an induction heating coil that displays superior safety/reliability, even if it is an induction heating coil which turns into one making a large output by diagnosing the induction heating coil from the outside, without disassembling it and early discovering an exfoliation part of the induction heating coil and an insulation member that is a main factor causing degradation, and also to provide its method.

The degradation diagnosis device is composed of a looseness meter 2 for measuring the degree of looseness of a coil package 1, and a diagnostic control part 3 connected thereto. The looseness meter 2 comprises a hammer 4 for striking the coil package 1 and an acceleration detector 5 for measuring vibration acceleration due to the striking sound, when the hammer 4 strikes the coil package 1. The looseness meter 2 quantitatively finds the degree of the looseness (namely, the exfoliation degree of a coil 1b and a castable cement 1c of the coil package 1) of the coil package 1 from strength of striking due to the hammer 4 and a dimension of the vibration acceleration measured by the acceleration detector 5.