PURPOSE: To prevent burglary and stealing including the software of a computer main body from being performed by enabling a system to be operated normally only with a solid shape key with specific identification information owned by a valid user and disabling a system operation by a malfeasant third party by setting a power source compulsory disconnection mode by check for the validity of a user at (effective) in a portable computer easy to transport.

CONSTITUTION: This computer is provided with such feature that it is composed so as to operate a system normally only by the valid user by providing the solid shape key 41 provided with signal terminal parts 41a, 41b, a key interface part 40 provided on a device main body and provided with the housing part of rectangular parallelopiped key 41, and a processor 2 which judges validity for system use from the identification information of the solid shape key 41 read via the key interface part 40 and disconnects a system power source when validity is not confirmed, and presenting the solid shape key 41 to a system main body.