PURPOSE: To reduce a cost of manufacture so as to improve efficiency of manufacture by eliminating a loss of transmission according to an automatic stepless speed changer in the past, and improving efficiency of fuel consumption, also to form various gears in the past into a combined simplified structure.

CONSTITUTION: Power is transmitted from a power input shaft 1 to a propeller shaft 8, to rotate the propeller shaft 8, and by rotating the propeller shaft 8, a base unit 9 is rotated similarly to the propeller shaft with the power shaft 1 and the propeller shaft 8 serving as the center. While rotation of the base unit 9 approaches to and separates from a rotational speed of the power shaft, rotational ratio of the power input shaft to the propeller shaft is changed steplessly by gears 3 to 7.