A ring segment and a turbomachine including the ring segment are provided. The ring segment installed on an inner circumferential surface of a casing and disposed to face an end of a blade disposed inside the casing, the ring segment includes a segment body disposed inside the casing in a radial direction of the casing and including a plurality of cooling channels through which cooling air flows, a pair of segment protrusions protruding outward from the segment body, coupled to the inner circumferential surface of the casing, and spaced apart from each other in a flow direction of fluid flowing through the casing to form an RS cavity into which cooling air is introduced, wherein when the segment body has a cross section along an imaginary plane including a radial straight line of the casing, the cooling channel is formed such that a width in a direction perpendicular to a radial direction of the casing is greater than a width in the radial direction of the casing.