To provide a computer system for making it impossible to use an in-circuit emulator(ICE) device in a security environment, and making it possible to use the ICE device in a manufacture environment or a non-security environment.

This processor is integrated with a special S latch which can be set according to a security signal. In one state of the S latch, the processor is set so as to be put in a security mode where only an instruction is performed, and any command from an ICE device is not performed. In the second state of the S latch, the processor is set so as to be put in a non-security state. Security data read by a boot block code stored in a BIOS storage device are written in a non-volatile random access memory(NVRAM). The book block code is made operable so that the security data in the NVRAM can be read, and the S latch is set so as to be put in a proper security state.