To solve the problem that when a hydrostatic stepless transmission is mounted in parallel with a dual clutch type transmission capable of continuously changing speed in a large-sized work vehicle, a favorable exchangeability therefor or the like is required, while in a small-sized work vehicle, due to its small mounting space, for accommodating the hydrostatic stepless transmission and a transmission mechanism other than the same, the transmission mechanism is required to be arranged at an adequate position in relation to an input shaft of the hydrostatic stepless transmission.

In a transmission 2 provided with the dual clutch type transmission 5 in a transmission case 3, a removable structure 23 is provided that enables removal of the hydrostatic stepless transmission 4 from an engine output shaft 7 and a sub-speed changing input shaft 24. Meanwhile, in a transmission 241 provided with, in a transmission case 246, a forward/backward traveling selector unit 247 having a clutch shaft 295, a counter shaft 297 and the like substantially parallel to a speed-changing input shaft 251, the forward/backward traveling selector unit 247 is arranged within a width between both ends of the speed-changing input shaft 251 when viewed in a direction orthogonal to the speed-changing input shaft 251.