To provide a transmission having less power loss and excellent accelerating ability from standstill.

This transmission can change a torque transmitted from a power source 1 to an output member 18 according to the discharge amounts or discharge pressures of fluid pressure pumps 12, 13 having also motor functions. The transmission comprises a differential mechanism 4 to which a torque is transmitted from the power source 1, first transmission mechanisms 21, 22, 23 disposed between an output element 4C and an output member 18 and setting predetermined reduction gear ratios, an engagement mechanism 26 bringing the first transmission mechanisms 21, 22, 23 into a state of being capable of selectively transmitting a torque between the output element 4C and the output member 18, a fluid pressure motor 12 outputting a torque by its operation by receiving the pressure fluid discharged from the fluid pressure pump 13, and a second transmission mechanism 24 installed between the output shaft 9 of the fluid pressure motor 12 and the output member 18 and setting a reduction gear ratio larger than that by the first transmission mechanism.