A protective cover structure includes a protective cover that is fitted to an assembly work opening disposed in a wall of a case in which electric components are accommodated, thereby closing the opening, and a fitting detecting connector that detects that the protective cover is fitted to the assembly work opening. The fitting detecting connector includes a receptacle connector which is fixed to an interior of the case and an insertion/extraction connector which is disposed on the protective cover in a mutually insertable/extractable manner while being opposed to the receptacle connector. The receptacle connector includes a tubular housing and fitting detecting conductors in the tubular housing. The insertion/extraction connector holds a pair of detecting electrodes which are electrically conductible with the fitting detecting conductors, and is molded integrally with the protective cover.