To solve a problem that a conventional hybrid drive system for a working vehicle in which the motive power of an electrically operated motor is assembled to the motive power of an engine to drive a vehicle shaft and a PTO shaft (power take-off shaft) causes a large difference in an operation feeling in the operation of the transmission before and after switching over motor drive and engine drive, because only a gear type stepped variable transmission is interposed in a train from the engine to the vehicle shaft and the PTO shaft when driving the engine although a generator and electrically operated motor line operates as a kind of a stepless transmission when driving the motor.

A main transmission 14 as the stepless transmission is interposed in a traveling drive train 52 for transmitting the motive power from the engine 3 to the rear wheels 7, 7. A motor generator 4 is provided in the most upstream position of a power transmission path in both trains of the traveling drive train 52 and the PTO system train 53 for transmitting the motive power from the engine 3 to the PTO shaft 11.