Abstract: The ventilating fan system comprises an air flow passage including a duct for guiding the air in a room to outside and a ventilating fan arranged in the air flow passage; whereby said ventilating fan is an inversion type ventilating fan, in which opposed rotating blades arranged in a direction perpendicular to flowing direction of the air are rotated in reverse directions, and the ventilating fan is arranged at an end portion of the air flow passage closer to outside and sucks the air in the room and discharges it to outside.