By assigning presentation process information, which is used for changing a game screen or a game sound to a game screen or a game sound that is different from an ordinary game screen or game sound, to a player through an external storage medium when a predetermined condition is satisfied, a network game system and a client game device capable of increasing the attraction and strengthening the friendship between players are provided. In a network game system including game devices each including a unit that reads out a player ID from an external storage medium and a server terminal that is communicably connected to the game devices through a network, presentation process information used for performing a game presentation associated with a game presentation ID at the time of performing a game is stored in a managing section, the game presentation ID set to be used in the external storage medium based on the player ID is stored in the managing section in association with the player ID, and, when a predetermined condition is satisfied, information on the use permission setting of the game presentation ID that is stored in the managing section is updated.