To provide a technology for using an end batch processing service to a plurality of transaction systems by a mediator system without registering all the information on a user system in the mediator system.

This method comprises a step for receiving authentication information stored in a user system and the provision request of a specific service from the user system, a step for connecting a mediator system to a plurality of transaction destination systems by using the authentication information acquired from the user system and authentication information stored in the mediator system, a step for requesting the execution of specific processing corresponding to the specific service to each of those connected transaction destination systems, a step for receiving the processing result of the specific processing transmitted from each transaction destination system to the mediator system, and a step for generating the provision result of the specific service by using the received processing result of each transaction destination system, and for transmitting the generated specific service provision result from the mediator system to the user system.