Abstract: Disclosed is an infinitely variable speed transmission, including: a speed changing mechanism for primarily changing power from an engine into a necessary speed ratio, including: a sun gear disposed on an input shaft for transmitting power generated from the engine; a plurality of planet rollers which are disposed around the sun gear at a predetermined distance from each other, each planet roller having a truncated cone-shape and being revolvable around the sun gear and rotatable about its axis; a carrier for connecting the planet rollers with each other; a movable ring disposed to be circumscribed on outer tangential line of the planet rollers and movable by moving member along a longitudinal direction of the planet rollers to change a rotational speed of the planet rollers by varying an operating diameter so that an output speed outputted through the carriers connecting the planet roller with each other can be varied; and a second speed changing mechanism for changing the output speed from the speed changin