PROBLEM TO BE SOLVED: To easily change services to be provided on a system by coordination between a video-displaying device and a portable terminal, efficiently collect information on the use states of the services while keeping the reliability and durability of the information, and charge on a metered rate. SOLUTION: An application, which is executed in a display device 141 installed on a customer site, gives the degrees of importance to logs and outputs them. A state of a network (a communication speed) between the display device 141 and a management server 101 of a service-providing firm, to which the logs are to be transmitted, is monitored. When the state of the network is over a preliminarily fixed standard, all or some of the logs are transmitted. When the state of the network is at the preliminarily fixed standard or less, only log information or generated hash values is transmitted to store log main parts in a memory card 110 or the like. Afterward, the contents of the memory card 110 are compared with the hash values preliminarily transmitted to the server to detect falsification of data. COPYRIGHT: (C)2007,JPO&INPIT