An RPC conversion processing system (10) that performs relaying between a first application (70) and second application (80) of different protocols. The RPC conversion processing system includes a first interface provider (20) connected to the first application and configured to provide a first interface for the first application, an RPC conversion relay function section (40), and a second interface provider (30) connected to the second application and configured to provide a second interface for the second application. The first interface provider receives a request for processing an RPC from the first application. The RPC conversion relay function section converts the RPC into an RPC of the second application and outputs the RPC of the second application to the second interface provider, thereby relaying an RPC between the first application and the second application.