Game machines automatically change the difficulty level of the game operation in the middle of the game based on an evaluation made on a player's game operation. A game machine determines, at least in terms of timing and type, whether the player's inputted button operation matches with the button operation designated by the game. If there is a match, the game machine determines it as an operation success. If not, the game machine determines it as an operation error. Based on the degree of operation success or operation error, the game machine dynamically changes the difficulty level of the game operation in the middle of the game.