To provide an inexpensive power transmission with excellent torque transmission and capable of outputting high torque at a low speed and capable of starting, creep traveling and hill holding when it is applied to a vehicle in particular, and to improve on-vehicle property by miniaturizing and reducing weight.

This power transmission is provided with a planet gear PGS arranged between an input shaft 1 to which torque is transmitted from an engine and an output shaft 2 from which torque is output to an automatic transmission, a first clutch A-C/L arranged between the career 12 of the planet gear PGS and the input shaft 1, a second clutch B-C/L arranged between the career 12 and the output shaft 2, a third clutch C-C/L arranged between a sun gear 11 and the input shaft 1, and an one-way clutch OCL capable of changing over a ring gear 13 to be fixed/unfixed.