To provide a function extension unit robbery protection device protecting function extension units such as PC card, HDD, etc., inserted in an extension slot of note book personal computers from robbery.

In the case a function extension unit inserting and fitting in the extension unit 2 of a personal computer body 1 is PC card 3, the personal computer body 1 has a main lock mechanism 5 locking and unlocking the computer and close at least a part of unit insertion inlet of the extension slot with a robbery protection cover member 4 linking the rotation operation of locking and unlocking the main body locking mechanism 5. It also has a rotation lock nail 6 detaching the robbery protection cover member 4 linking the rotation operation of the main lock mechanism 5 and by the coupling force of the rotation lock nail 6 resisting a return spring 7, the robbery protection cover member 4 slides in the left direction of the figure for closing a part of the unit insertion inlet of the extension slot 2. By this, a robbery intentionally taking the PC card 3 out of the extension slot 2 is prevented.