To improve transmission efficiency while enlarging the range of a gear ratio of a gear ratio infinitely continuously variable transmission.

A first variable speed mechanism comprises a continuously variable transmission, and a second variable speed mechanism comprises a transmission capable of connecting and disconnecting rotation between input and output and realizing two large and small gear ratios. The output part of the first variable speed mechanism is connected to a sun gear of a planetary gear mechanism and to a ring gear through a clutch. The output part of the second variable speed mechanism is connected to a carrier of the planetary gear mechanism. The ring gear is connected to the output shaft side for driving a driving wheel. It is constituted to have the relation of Ig2/Id<λ1(1+α)/(λ1/λ2+α) among the maximum gear ratio λ1 and minimum gear ratio 12 of the continuously variable transmission, the smaller gear ratio Ig2 of the second variable speed mechanism, the number-of-teeth ratio α between the number-of-teeth of the sun gear of the planetary gear mechanism and the number-of-teeth of the ring gear, and a rotation ratio Id between the sun gear input rotation of the planetary gear mechanism and the output rotation of the continuously variable transmission.