A control unit mainly includes game condition judging means, moving period determining means for determining a moving period T0 of a ball object, first operation response period determining means for determining a first operation response period T1 of a bat object, which begins at a first operation response start opportunity St1 preceding a pitching end opportunity E0 of the moving period T0, second operation response period determining means for determining a second operation response period T2 of the bat object, which begins at a second operation response start opportunity St2 succeeding the first operation response start opportunity St1, operation input opportunity receiving means for receiving a operation input opportunity HP of a controller, and operation opportunity response judging means for judging whether the operation input opportunity HP is included in either the first operation response period T1 or the second operation response period T2.