A fresh airflow is conducted from a supply air chamber through nozzles into a ring-shaped mixing chamber. A circulated airflow is conducted from a room space into a cylindrical suction chamber inside a ring-shaped heat exchanger. From the suction chamber the circulated airflow travels through the heat exchanger into the mixing chamber. The nozzles are located in the upper part of the mixing chamber at a distance from each other on the periphery of at least one circle, whereby the mid-point of the circle is located on the vertical central axis of the supply air terminal device. The horizontal component of the direction vector of the fresh airflow discharging from each nozzle forms an angle β, which is in a range of 45-135 degrees, with the radius of said at least one circle, and the direction vector is directed downward, in relation to the horizontal plane at an angle α, which is in a range of 15-75 degrees, whereby a rotating airflow directed downward is formed in the mixing chamber.