Recently, information system operation becomes more important because of increasing size of information system and outsourcing the system operation. However, it is not easy for customers to judge the validity of the system operation cost. To provide information which helps the judgment, we analyzed factors which affect system operation cost. Working time of system operation service provider has the strong relationship to the cost. So, if customers know the working time, they estimate the cost properly. However, it is difficult for customers to know the working time generally. So, we assumed that customers estimate unit cost and working time, to speculate total operation cost roughly. To help the estimation, we analyzed factors affected working time and unit cost. The analysis results show that working time is settled based on the software size and the number of users, and the unit cost of the engineers increases when network range of the system is wide.