PROBLEM TO BE SOLVED: To improve the outside air suction efficiency of a cooling fan by decreasing the clogging of a filter body, and to prevent the output reduction or overheating of an engine.SOLUTION: A clutch (C) is provided, which connects and disconnects the transmission of driving force from an engine (E) to a cooling fan (10). A ventilation device (17) sending air from the inside to the outside of a filter body (8B) for dustproof, is provided so as to freely enter a space portion (11) formed between a radiator (9) and the filter body (8B). A prime mover for a working vehicle is linked so as to be disconnect the clutch (C) with a predetermined delay since the ventilation device (17) enters the space portion (11), thereby stopping a cooling fan (10) and starting ventilation from the ventilation device (17). A bypass route (12) is provided, which introduces outside air to the cooling fan (10) by bypassing the filter body (8B), while the ventilation device (17) enters the space portion (11).SELECTED DRAWING: Figure 5
