The invention provides a ventilation device used for a portable house. A simultaneous-use type ventilator, a motor, an upper belt wheel, a large gear, a lower belt wheel, a small gear, an outer coverand an inner gear ring are included; the inner gear ring is fixed to the right side face of the outer cover; the center position of the left side face of the outer cover is provided with an open groove in which a rotating shaft is arranged; the right end of the rotating shaft extends to the right side of the inner gear ring; the lower belt wheel is installed at the right end of the annular side face of the rotating shaft; the annular side face of the portion, on the left side of the lower belt wheel, of the rotating shaft is connected with the small gear; the large gear is installed at the left end of the annular side face of a connection shaft; the large gear is engaged with the small gear and the inner gear ring through gear teeth; the motor is fixed to the upper side of the outer coverthrough a fixed base; the upper belt wheel is installed on the portion, on the right side of the inner gear ring, of the motor; and the upper belt wheel is connected with the lower belt wheel througha transmission belt. The design achieves the function that several rooms share one ventilation device, and the ventilation device is convenient to use, capable of saving material resources and achieving intermittent ventilation, and safe and reliable.