Abstract: Multiple shops exist in a virtual space of a game. Each shop belongs to any one of multiple unions. When a player character buys or sells a game item at any of the shops, a power point value of the union to which the shop belongs is increased according to the sales amount. The higher the power rank of the union to which the shop belongs becomes, the more the types of sellable and buyable game items are increased. The higher the power rank of the union to which the shop belongs becomes, the more cheaply the player can buy the game item and the higher the amount the player can sell the game item. The higher the power rank of the union where the shop belongs becomes, the more points that are given to a point card according to the buying or selling of the game items.