Provided is a ventilation device equipped with a housing, a heat exchanger installed in the middle of the inside of the housing, an indoor air exhaust port and an outdoor air suction port formed at one side of the housing based on the heat exchanger, an indoor air suction port and an outdoor air supply port formed at another side of the housing, an exhaust fan installed at one side of the interior of the housing for exhausting indoor air through the indoor air exhaust port to outside, a supply fan installed at another side of the interior of the housing for sucking outdoor air from outside and sending the outdoor air to the outdoor air supply port, and a brushless DC (BLDC) motor for driving the exhaust fan and the supply fan. The ventilation system includes a motorized damper installed at each of the indoor air exhaust port and the outdoor air suction port for adjusting the amount of indoor air exhausted by the exhaust fan and the amount of outdoor air sucked by the supply fan; an RPM sensor embedded in the BLDC motor to measure revolutions per minute (RPM); and a microprocessor configured to receive a signal regarding the RPM of the BLDC motor measured by the RPM sensor and adjust an opening ratio of the motorized damper.