The present invention relates to a prime mover portion structure of a working vehicle, the goal is to enhance the cooling efficiency of the working vehicle engine. To achieve this goal, a hydraulic type stepless speed changing device (30) for changing the speed of the driving force of the engine (20) and outputting to forward direction and reverse direction is disposed； an axis of a rotating shaft (41) of a fan (40) is disposed at the location deviated from the axis of the output shaft (33) of the hydraulic type stepless speed changing device (30)； and a first transmission device (250) is disposed to couple the output shaft (33) and the rotating shaft (41). Through the speed changing action of the hydraulic type stepless speed changing device (30), the fan (40) can be freely changed into a cooling status in which the fan (40) is driven in forward direction to suck external air inwardly from the outside of the filtration bodies (12A, 12B, 12C)； or a dust removing status in which the fan is driven in reverse direction to blow internal air outwardly from the inside of the filtration bodies (12A, 12B, 12C).本發明涉及作業車輛的原動部結構。目的是提高作業車輛的發動機冷卻效率。解決方法是設置將發動機(20)的驅動力向正轉方向及反轉方向變速並輸出的液壓式無級變速裝置(30)，將風扇(40)的旋轉軸(41)的軸心配置在偏離液壓式無級變速裝置(30)的輸出軸(33)的軸心的位置，設置使上述輸出軸(33)和旋轉軸(41)聯動的第一傳動裝置(250)，通過上述液壓式無級變速裝置(30)的變速動作自由轉換成：將風扇(40)向正轉方向驅動，從過濾體(12A、12B、12C)的外側向內側吸入外部空氣的冷卻狀態；以及將該風扇向反轉方向驅動，從過濾體(12A、12B、12C)的內側向外側吹出內部空氣的塵埃去除狀態。
