Server device, non-transitory server device-readable storage medium, and game system

A non-transitory computer-readable storage medium with a game program stored thereon, the game program instructing an electronic game server device having a processor, a memory, and being connected to one or more player terminals over a network, to execute the following processes:

• a process to store in a storage unit trade information related to a trade for exchanging an item in an exchange source for an item in an exchange target, and player information in which each of items owned by players is associated with each of the players and is used in an electronic game to give the players advantages in game progress;
• a process, when a manipulated input performed by a player who accepts to exchange the item in the exchange target based on the trade is received, to judge whether or not the player owns the item in the exchange target based on the player information;
• and
• a process to generate data of a game screen for purchase for allowing the player to purchase the item in the exchange target in a case where it is judged that the player does not own the item in the exchange target,
• the trade information including an exchange amount that is associated with each of the items in the exchange source and each of the items in the exchange target,
• the player information including the number of items that is associated with each of the items owned by the players,
• the game program further instructing the computer to execute,
• a process, when a manipulated input performed by a player who accepts to exchange the item in the exchange target based on the trade is received, to judge whether or not the number of the items in the exchange target owned by the player is more than the exchange amount of the items in the exchange target based on the player information and the trade information;
• and
• a process to generate data of a game screen for purchase for allowing the player to purchase the number of the items in the exchange target required to be added in a case where it is judged that the number of the items in the exchange target owned by the player is less than the exchange amount of the items in the exchange target.