There has been proposed a system which, when a user has achieved a mission set in a video game, grants the user a trophy as a virtual prize for the mission accomplished (see PTL 1). The trophies won by the user on the game machine may be registered with a server connected to the Internet when the user signs in to a relevant network service. The registration allows trophy acquisition information to be synchronized between the game machine and the server. It has become common practice that the high-speed network environment, which has been provided in recent years, enables the users operating their game machines to exchange diverse kinds of information data between them.