Apparatus for incorporating lock plates in video cassettes

A lock plate which comprises a plate body having protrusions, a shaft combined with and extending parallel to the plane of the plate body, and a torsion spring having a coiled portion engaged with the shaft is incorporated in the cassette case body of a video cassette in order to allow a guard panel to be locked in a closed position. The guard panel is mounted on a surface of the cassette case body, along which surface the magnetic tape slides. An apparatus for incorporating a lock plate in a video cassette comprises a plate holding device which holds the lock plate in an inclined orientation so that the surface of the plate body, on which surface the protrusions are formed, faces down obliquely and so that the shaft extends horizontally above the plate body. A fitting device grasps the lock plate held by the plate holding device, moves it linearly while keeping it in the inclined orientation, and thereby fits it into the cassette case body.