A user of services is enable to utilize a highly value-added service employing secret data of the user without presenting the data to the service provider side. In a system in which a server is coupled with a client via a communication network, the client inputs and sends a service identifier to the server, receives a program to execute the service from the server, inputs secret data as client controlled data from an input device and sends a server control data request to the server, and then receives the requested data from the server. The input data is irreversibly processed by use of the program and received data such that the client sends results of the process to an expert on the server side to receive an advice of the expert. By referring to the advice, the service user inputs evaluation of the outputted results. The steps beginning at the data request input are repeatedly conducted until the evaluation becomes satisfactory, thereby transmitting the process results to the server.