To provide a working vehicle running speed change control device capable of performing running speed change control against load fluctuation with a relatively inexpensive structure without using any electric control system.

The working vehicle running speed change control device comprises a variable capacity type hydraulic pump 35 to change the swash plate angle by a speed change operator 55 and main and sub hydraulic motors 36 and 37 connected to the hydraulic pump 35 in parallel, and the rotational output of the hydraulic motors 36 and 37 is transmitted to a common output shaft 32. The main hydraulic motor 36 is of a constant capacity type in which the swash plate angle is fixed, and the sub hydraulic motor 37 is of a variable capacity type in which the swash plate angle is variable by a control piston 38. The control piston 38 is connected to a pressurized oil feed passage 39 to the hydraulic motors 36 and 37 so that the swash plate angle of the sub hydraulic motor 37 is changed and controlled in the capacity increasing direction as the feed pressure to the control piston 38 is increased.