To use commercial software, most software users purchase the software. Some software users, who do not use the software frequently, regard purchasing the software as undue expense. Software rental service can be an effective substitute. To support the software rental service, charging scheme is necessary. Two categories of charging scheme can be considered. One is charging a fixed amount of fee for a fixed period of time and the other is charging a fee based on the actual usage time. In this paper, the software pay-per-use approach based on the amount of time that the software user has used is proposed. The proposed approach gives the capability to calculate the usage time.