A mobile telephone includes a CPU that obtains and decodes instructions included in an OS, a nonsecure program, a switch device driver, and a secure program, and operates according to the decoding results. A memory includes a controlled area and an uncontrollable area. The OS has only the controlled area as its access space, and includes an instruction for mediating access of the nonsecure program to the controlled area and an instruction for instructing the switch device driver to make a switch to the secure program. The nonsecure program includes an instruction to access the controlled area via the OS. The switch device driver includes an instruction to make a switch from execution of the OS to execution of the secure program in response to an instruction of the OS. The secure program has only the uncontrollable area as its access space, and includes an instruction to access the uncontrollable area.