An inner reel is provided with an A-zone, a B-zone and a C-zone. Symbols of the inner reel are arranged in the respective zones. The A-zone to the C-zone are selectively displayed in accordance with a game condition. The A-zone is used in a normal game. The B-zone and the C-zone are used for deciding a sort of benefit to be afforded in a free game. Either of the B-zone or the C-zone is used in the free game. Using the B-zone brings the benefits in that winning provability is raised and in that odds are increased in case of winning. Using the C-zone brings the benefit in that a number of the free games are added.