A deposit managing unit 22 receives a game player's deposit command transmitted from a terminal device 12 and deposits virtual currency in a deposit amount specified by the game player according to the received deposit command. In addition, the deposit managing unit 22 prohibits the game player from using the virtual currency deposited by the game player until a predetermined deposit period expires. When a depositing game player deposits virtual currency, a benefit offering unit 24 offers the depositing game player a benefit that gives a higher advantage to the depositing game player in battle until the deposit period expires in comparison to a case where the depositing game player does not deposit virtual currency.