To provide a theft preventing device easy to fit and reliably preventing a theft by storing a computer code storage device in a lockable case having a theft preventing wire, and connecting the case to a main body with connectors.

A case (f) made of a strong material is provided with an opening/closing cover having a key (e), a wire (i) for mooring the case (f) to a fixed object such as a column so that the case (f) cannot be moved, and connectors (c), (c') and fixing screws (d) so that the case (f) can be easily connected to a computer or a computer related apparatus. A program theft preventing device and a code collating circuit (g) are stored in the case (f), and the case (f) is locked by the key (e). The device in the case (f) is interlocked with the key (e) so that the device is not operated without the key (e), and the connector (c) is not released without the key (e). When the case (f) is fitted, no machining is required at all on the computer side. The theft or surreptitious use of the related apparatus can be reliably prevented.