Provided is a semi-cylindrical osteotomy device including: a guide portion where a tibia accommodating space in which a tibia is accommodated is formed; a cutter portion moving in the tibia accommodating space and cutting the tibia while moving along an inner circumferential surface of the guide portion; and a driving unit driving the cutter portion. According to the semi-cylindrical osteotomy device, stability of a surgery is increased by inserting the guide portion by approaching a side surface of the tibia to minimize an exposed portion of a bone. Also, a wire saw moves along a slit of the guide portion, and thus a cut bone surface of a semi-cylindrical shape is easily and quickly formed.