A transmission M of a vehicular power transmission system has a first shifting part and a second shifting part which shift a power of an internal combustion engine, a first shift clutch transmitting and interrupting the power to the first shifting part, and a second shift clutch transmitting and interrupting the power to the second shifting part. A start clutch transmitting and interrupting the power to the first shift clutch and the second shift clutch is constructed of a centrifugal clutch C having a clutch shoe. The resulting configuration provides a vehicular power transmission system which has excellent efficiency of power transmission and durability, as well as being capable of being manufactured at low cost, and being capable of relieving a start shock.