[Object] To enhance power transmission efficiency and to reduce a shift time lag. [Means to achieve the object] A power transmission has a start clutch (2) capable of transmitting or cutting off power from the engine to wheels at any time, a plurality of gear stage clutches(3), each gear stage having a predetermined gear ratio and a gear select stage (5) where any gear ratio of power transmission from the engine (E) to the wheels can be selected. The gear stage clutch (3) has a plurality of alternately arranged driving plates and driven plates and an oil piston hydraulically operable to engage/disengage the plurality of driving plates and driven plates, thus enabling to transmit power at a predetermined gear ratio.
