To improve the interest of a game by making play various by preventing the number of medals to be acquired in the occurrence of a bonus mode from being uniform and to more improve the interest of the game by effectively utilizing the characteristics of a player.

In the case of success based on big bonus picture patterns, before transiting to a BB mode game, a middle reel is automatically or manually stopped, a lottery game different from unit play is performed, the value of a BB acquisition counter in the BB mode game and the value of a BB execution counter are determined and afterwards, the BB mode game is started. Thus, the number of medals to be acquired is changed each time the bonus mode occurs.