A game system includes a plurality of game cards, a game cartridge and a game machine. Each game card visually portrays a figure of a character, stores ability data for the character, and mechanically readably records an identification code and individuality expressing data of the character. The game information storage medium stores a game program for generating at least some of the characters of the game cards in an image display game. The game machine receives therein the game information storage medium. The game machine includes a CPU to execute a game program for an image display game. The game information storage medium is provided with a data reader to read out the identification data and individuality expressing data of the character recorded on the game card. The CPU, when supplied with the identification data and individuality expressing data from the reader, adds the individuality expressing data to the game program thereby executing a game process for the image display game.