A wiper system is characterized by its continuous reversing movement. This means that a wiper motor is repeatedly subjected to forward and reverse loads under the influence of the variable load which a wiper blade receives when moving on the glass surface, and of the weight of a wiper arm and blade. Consequently, the system generates reversing sound inside the motor, i.e., collision sound between gears resulting from backlash. This is a challenge to be overcome.In this study, the authors have established a new backlash-less and high-efficiency reduction gear structure by adopting pinion gears that can move in response to the load variations at reversing in the existing double worm gear reducer. With this structure, the growing needs for noise reduction, downsizing and weight saving of wiper motors can be met concurrently.