An air conditioner installed embedded in the ceiling of an air conditioned room, comprising: - a casing comprising: a casing lower part (3, 7) formed by an alternating sequence of a plurality of side parts (30a - 30d) and a plurality of corner parts (30e - 30h); side part outlets (12a - 12d) disposed along each of said side parts; corner part outlets (12e - 12h) disposed at at least one of said plurality of corner parts; and an inlet disposed so that it is surrounded by all of said side parts; and - a fan, disposed inside said casing, that sucks in air from said inlet into said casing, and blows out the sucked in air from said side part outlets and said corner part outlets into said air conditioned room; characterized in that - the dimensional relationship between each said corner part outlet and the side part outlets adjacent to said corner part outlet is: D / L 1 W 1 + S 2 0.5 > 0.15 where D is the distance between a first proximate part, which is the most proximate part of each said corner part outlet to each said side part outlet, and a second proximate part, which is the most proximate part of each said side part outlet to each said corner part outlet, L 1 is the length of each said side part outlet in the direction along an outer circumferential edge of said side part, W 1 is the width of each said side part outlet in the direction orthogonal to the outer circumferential edge of said side part, and S 2 is the opening area of each said corner part outlet, and - horizontal flaps capable of oscillating about an axis in the longitudinal direction are provided at the side part outlets, the wind direction of the air blown out from the side part outlets into the air conditioned room is varied by the horizontal flaps, and the air blown out from the corner part outlets into the air conditioned room is blown out in a fixed direction. - a casing comprising: a casing lower part (3, 7) formed by an alternating sequence of a plurality of side parts (30a - 30d) and a plurality of corner parts (30e - 30h); side part outlets (12a - 12d) disposed along each of said side parts; corner part outlets (12e - 12h) disposed at at least one of said plurality of corner parts; and an inlet disposed so that it is surrounded by all of said side parts; and a casing lower part (3, 7) formed by an alternating sequence of a plurality of side parts (30a - 30d) and a plurality of corner parts (30e - 30h); side part outlets (12a - 12d) disposed along each of said side parts; corner part outlets (12e - 12h) disposed at at least one of said plurality of corner parts; and an inlet disposed so that it is surrounded by all of said side parts; and - a fan, disposed inside said casing, that sucks in air from said inlet into said casing, and blows out the sucked in air from said side part outlets and said corner part outlets into said air conditioned room; characterized in that - the dimensional relationship between each said corner part outlet and the side part outlets adjacent to said corner part outlet is: D / L 1 W 1 + S 2 0.5 > 0.15 where D is the distance between a first proximate part, which is the most proximate part of each said corner part outlet to each said side part outlet, and a second proximate part, which is the most proximate part of each said side part outlet to each said corner part outlet, L 1 is the length of each said side part outlet in the direction along an outer circumferential edge of said side part, W 1 is the width of each said side part outlet in the direction orthogonal to the outer circumferential edge of said side part, and S 2 is the opening area of each said corner part outlet, and where D is the distance between a first proximate part, which is the most proximate part of each said corner part outlet to each said side part outlet, and a second proximate part, which is the most proximate part of each said side part outlet to each said corner part outlet, L 1 is the length of each said side part outlet in the direction along an outer circumferential edge of said side part, W 1 is the width of each said side part outlet in the direction orthogonal to the outer circumferential edge of said side part, and S 2 is the opening area of each said corner part outlet, and - horizontal flaps capable of oscillating about an axis in the longitudinal direction are provided at the side part outlets, the wind direction of the air blown out from the side part outlets into the air conditioned room is varied by the horizontal flaps, and the air blown out from the corner part outlets into the air conditioned room is blown out in a fixed direction.