PURPOSE: To secure fairness of game conditions in a variation winning device by detecting a prize ball in the variation winning device by an entering ball sensor, calculating variations by numerical value calculating means, and judging a winning by comparing the variation selected in association with an entering ball signal and a judgement value.

CONSTITUTION: When a control unit 30 judges that a special game condition is satisfied, the number of entering balls, the number of openings, and a winning flag are reset to zero. A solenoid 38 is driven, thereby opening a big winning prize mouth, and the number of openings is increased. The control unit 30 subsequently judges the presence or absence of an entering ball signal from a proximity switch 24 which is outputted every time when a prize ball enters the big winning prize mouth. When the entering ball signal is inputted, the number of balls entering the big prize mouth is increased. Subsequently, it is judged that the number of balls to a variation winning prize device 10 is equal to, for example, 10 or less. When it is equal to 10 or less, it is judged whether the winning flag is set to 1 or not. A count value of a counter 36 is read out and when the count value is equal to 0, the winning flag is set to 1 and a display light 20 is turned on.