Recently, one-way car-sharing service that allows a user to drop the vehicle off at the destination has been started. However, it has not been as popular as expected mainly because it cannot assure the existence of an available vehicle at the start station or a vacant parking slot at the destination station. At this moment, the company staff are responsible for moving the vehicles to certain stations manually. Therefore, it is very costly. In order to reduce costs and make more efficient use of vehicles in one-way car-sharing service, we propose to involve a future potential user to move vehicles. We assume that there exist some requested one-way trips. Our method inserts a new trip among the existing trips for maximizing the number of successful trips. This trip is called 'a system request trip.' We assume that the system request trip can be realized by changing a future schedule or asking future potential users who want to get some rewards. In this paper, we analyzed how each user uses vehicles in one-way car-sharing service by using the past data of demonstration experiment conducted by a car-sharing company in Tokyo, Japan. Based on the analysis result, we examined how to request each user.