PURPOSE: To prevent the faulty use of a computer by reading an applicable time point, etc. of a computer which is previously set and comparing the read-out time point with an internal hard timepiece to decide the propriety for use of the computer.

CONSTITUTION: A main memory 1 is provided together with a central processor 2, and a computer aplicable time table 111 is set in an OS area 11 on the memory 1. While the processor 2 contains a hard timepiece 21. In an OS stop processing mode, the OS gives an input indication to an operator for the next application time point of the computer. Then a time point is typed in and stored to the table 111. In an OS rise processing mode, the OS reads an applicable time point out of the table 111 to a general-purpose register 22. This time point is compared with the timepiece 21 by a comparator 23. Then a signal OSOK is delivered if said time point is later than the timepiece 21, and the OS works to produce a system delay.