Transparent blank symbols are disposed on each of first, second and third display parts respectively provided in first, second and third display plates. The player wins if the same symbols of the first to third display parts are arranged in line on any of winning lines when the first to third display plates stop rotating. When the blank symbols of the first to third display parts are arranged in line on any of winning lines, the reel mounting plate starts rotating until the sub reel reaches the position behind the blank symbols. Then, the sub reel rotates and stops to display move and stop of the symbols. The symbol on the sub reel is observable through transparent parts in the blank symbols.