A positive crankcase ventilation system includes a positive crankcase ventilation valve, a coupling part, and a plate member. The coupling part is configured to couple the positive crankcase ventilation valve and an internal combustion engine. The plate member is attached to the coupling part on an opposite side from a side where the coupling part and the internal combustion engine contact each other. A portion of the plate member is bent in a direction toward a base of a hose insertion port provided on the positive crankcase ventilation valve, and another portion of the plate member is bent in a direction toward a side wall of an attachment portion of the positive crankcase ventilation valve provided on the coupling part.