To provide a ventilation device capable of executing humidification of indoor air only through circulation of the indoor air without introduction of outdoor air. This ventilation device comprises an electro-heat exchanger set within a main body and including a first air passage and a second air passage mutually crossing in partitioned states; an air supply passage formed within the main body so that outdoor air flows indoors through the first air passage of the electro-heat exchanger; a first blowing fan set in the air supply passage; an exhaust passage formed within the main body so as to discharge the indoor air through the second air passage of the electro-heat exchanger; a second blowing fan set in the exhaust passage; a humidifying rotor provided on the downstream side of the electro-heat exchanger in the air supply passage; a bypass passage formed between the exhaust passage on the upstream side of the electro-heat exchanger and the air supply passage on the downstream side of the electro-heat exchanger; a first damper opening and closing the bypass passage; and a second and a third dampers opening and closing the outlet of the exhaust passage and the inlet of the air supply passage, respectively.