A gaming system of the present invention includes: an input device which starts a base game awarding a payout according to a given winning; a data storage device storing special game condition data which defines, within a given value range, a plurality of sub ranges respectively allotted to special game conditions or “No Special Game” meaning no special game is run, each of the special game conditions being associated with an average payout different from those associated with the other conditions. In the system, a random number is sampled based on an input from the input device. A base game is run using the random number, and a payout according to a resulted winning is awarded. One of the sub ranges each allotted to one of the special game conditions or “No Special Game” is selected, based on a given condition with reference to the random number and the special game condition data. When the selected sub range is allotted to a special game condition, the special game is run under that special game condition and a payout is awarded.