PURPOSE: To specify a computer to be used and to strictly protect the software by providing a limit means which sets previously the limit frequency of the software with use of a communication means like a telephone circuit, etc., and inhibiting the execution of the software after the using frequency reaches the limit frequency.

CONSTITUTION: The data on the limit frequency is transmitted from a control computer 4 of a software offerer via a communication means and received by a computer system 3 of a software user. This limit frequency data is previously set to a limit frequency recording memory 12. Then the execution of the relevant software is discontinued after the using frequency of a user reached the set limit frequency. Thus it is possible to specify the computer that uses the software and to strictly protect the software.