A heat exchange element (6) which exchanges heat between indoor air and outdoor air during ventilation is provided at the position where a supply air passage (7) and a discharge air passage (8) intersect. A temperature detector (12) is provided in the discharge air passage (8) at the air discharge-side outlet of the heat exchange element (6), and when temperature detected by the temperature detection means (12) is lower than a predetermined value, a control unit (11) reduces the rotational speed of an air supply motor so that the flow rate of supply air is lower than the flow rate of discharge air. Thus, a heat exchange ventilator (1) is provided, which can continue the simultaneous operation of both air supply and air discharge while preventing the heat exchange element (6) from freezing.
