A belt-type stepless speed shifting transmission consisting of: (1) an input section having an input shaft with a rotational axis, a stationary pulley piece fixedly mounted on the input shaft, a pulley piece mounted on the input shaft and movable axially relative to the input shaft and stationary pulley piece with the stationary and movable pulley pieces cooperatively defining a groove for reception of a belt, and bearing structure for exerting an axial force on the movable pulley piece in the direction of the stationary pulley piece which axial force increases with the speed of the input shaft; and (2) an output section having an output shaft with a rotational axis, a second stationary piece fixedly mounted on the output shaft, a second pulley piece mounted on the output shaft and movable axially relative to the output shaft and second stationary pulley piece with the second stationary and movable pulley pieces cooperatively defining a groove for reception of a belt, a stop element, and cooperating cams on the second movable pulley piece and stop element for effecting relative axial shifting between the second movable and stationary pulley pieces upon the second movable pulley piece being rotated relative to the stop element.