There is provided a refrigeration cycle device that uses a refrigerant having a higher concentration than air under atmospheric pressure, and is capable of preventing a region having a certain refrigerant concentration or higher from being formed even if the refrigerant leaks in a casing of the refrigeration cycle device in a nonenergized state. To this end, the refrigeration cycle device includes: a casing having a first opening and a second opening, one of which is an inlet and the other of which is an outlet, and having therein an air course providing communication between the first opening and the second opening; and a refrigerant circuit provided in the air course in the casing and filled with a refrigerant having a higher concentration than air under atmospheric pressure, the casing having a third opening providing communication between the air course and outside of the casing, the third opening being arranged below the refrigerant circuit, and a lower edge of the third opening being located below lower edges of the first opening and the second opening, the refrigeration cycle device further comprising diffusion means configured to diffuse the refrigerant leaking from the refrigerant circuit and flowing from the air course through the third opening out of the casing.