A cassette adaptor is disclosed, in which a head cover for accommodating the magnetic head is elastically supported on the head spring in such a manner that the height of the recording head and the head gap on the signal transmission side can be automatically adjusted in accordance with the tape running position of the reproduction head of a cassette tape reproduction apparatus and in such a manner that the reels can be positively prevented from being driven under no load. The head cover includes a head guide in contact with a reproduction head and at least a dummy tape member in mesh with the tape guide of the cassette tape reproduction apparatus with the cassette adaptor mounted thereon. The head cover thus guides the magnetic head to a position opposed to the reproduction head.