A first symbol and a second symbol constituting a composition symbol "horse" are arranged on an inner reel and an outer reel respectively. When the outer reel is rotated and it is determined to display the composition symbol, the inner reels of first though third reel units are stopped so as to align the first symbols at a reference position, which is set relative to a central game line. After that, the outer reels of the first through third reel units are rotated and are stopped so as to align the second symbols on the central game line. When aligning the composition symbols "horse" on the central game line, the inner reel is rotated by a predetermined angle in forward and backward directions. This operation is carried out prescribed times to perform dynamic attraction in that pupil of the horse is changed.