Abstract: A stepless speed changing device is disclosed. The device converts its operational mode between three or four modes thus reducing the load applied to both the summarizer and the speed changing unit. First and second gears are fixedly and rotatably fitted over a torque input shaft, respectively. The second gear is selectively clutched by a first clutch to convert the operational mode into a third mode. Third and fourth rotatable gears of a driven shaft are selectively clutched by a second clutch to convert the operational mode into a first mode. The summarizer constructed of an epicycloidal gear train cooperates with the fourth gear in the first and third modes. A sixth gear of the driven shaft is selectively clutched by a third clutch to convert the operational mode into a second mode. An eleventh gear of the driven shaft is selectively clutched by a fourth clutch to convert the operational mode into a fourth mode.