Supply air terminal device, which is installable inside a false ceiling, comprising: - a cylindrical side wall, - a ring-shaped heat exchanger, which is located inside the cylindrical side wall, at a distance from the cylindrical side wall, - a radial cover plate, against which the top ends of the cylindrical side wall and of the ring-shaped heat exchanger are supported, - a ring-shaped mixing chamber, - a vertical central axis (Y-Y), - nozzles, which are placed 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 at least one circle is located on the vertical central axis (Y-Y) of the supply air terminal device, - a supply air chamber, from which a fresh airflow is conducted to the nozzles, - a bottom plate, which comprises at least a section of a periphery, in which there are an inner periphery and an outer periphery, - a ring-shaped output opening, which is located in the lower part of the mixing chamber and which comprises an inner periphery and an outer periphery, - a cylindrical suction chamber, which is formed in a space limited by the inner periphery of the heat exchanger and into which circulated air is drawn from the air-conditioned room space, characterized in that: - said ring-shaped mixing chamber is formed in a space restricted by the cylindrical side wall, the ring-shaped heat exchanger, and the cover plate, whereby the cylindrical side wall forms the mixing chamber's cylindrical outer side wall, the heat exchanger's outer periphery forms the mixing chamber's cylindrical inner side wall, and the cover plate forms the mixing chamber's roof plate, - the nozzles are placed on the periphery of said at least one circle in such a way that the horizontal (X-X) 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 circle, and the direction vector of the fresh airflow discharging from each nozzle is directed downward and forms an angle α, which is in a range of 15-75 degrees, with the radial plane formed by the radius of said circle, - whereby a rotating airflow directed downward towards the output opening is formed in the mixing chamber. - a cylindrical side wall, - a ring-shaped heat exchanger, which is located inside the cylindrical side wall, at a distance from the cylindrical side wall, - a radial cover plate, against which the top ends of the cylindrical side wall and of the ring-shaped heat exchanger are supported, - a ring-shaped mixing chamber, - a vertical central axis (Y-Y), - nozzles, which are placed 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 at least one circle is located on the vertical central axis (Y-Y) of the supply air terminal device, - a supply air chamber, from which a fresh airflow is conducted to the nozzles, - a bottom plate, which comprises at least a section of a periphery, in which there are an inner periphery and an outer periphery, - a ring-shaped output opening, which is located in the lower part of the mixing chamber and which comprises an inner periphery and an outer periphery, - a cylindrical suction chamber, which is formed in a space limited by the inner periphery of the heat exchanger and into which circulated air is drawn from the air-conditioned room space, - said ring-shaped mixing chamber is formed in a space restricted by the cylindrical side wall, the ring-shaped heat exchanger, and the cover plate, whereby the cylindrical side wall forms the mixing chamber's cylindrical outer side wall, the heat exchanger's outer periphery forms the mixing chamber's cylindrical inner side wall, and the cover plate forms the mixing chamber's roof plate, - the nozzles are placed on the periphery of said at least one circle in such a way that the horizontal (X-X) 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 circle, and the direction vector of the fresh airflow discharging from each nozzle is directed downward and forms an angle α, which is in a range of 15-75 degrees, with the radial plane formed by the radius of said circle, - whereby a rotating airflow directed downward towards the output opening is formed in the mixing chamber.