PURPOSE: To attain a keyboard lock during the usage of a task application program.

CONSTITUTION: When data indicating an invalidity are stored in a state storage area 7, a comparison means 8 outputs the data from a keyboard 3 to a CPU 9. On the other hand, when the data indicating a validity are stored in the state storage area 7, the comparison means 8 is operated in a secrecy protection mode, so that the data received from the keyboard 3 can be prevented from being outputted to the CPU 9. In the latter case, the comparison means 8 compares the data from the keyboard 3 with a password stored in a password storage part 5, and stores the data indicating the invalidity in the state storage area 7 when they are matched with each other. On the other hand, in the former case, the comparison means 8 compares the data from the keyboard 3 with the data stored in a key combination storage area 4, and transfers a control to a lock judging means 6 when they are matched with each other. When the data indicating the validity are stored in a password function state area 2, and the password is stored in the password storage area 5, the lock judging means 6 stores the valid data in the state storage 7.