Abstract: The head surface of the control signal head is formed into the curved surface such that the head surface of the control signal head has a first radius of curvature in the circumferential surface of the drum in the direction corresponding to the magnetic tape sliding direction, the first radius of curvature being slightly smaller than the radius of the drum, and such that the head surface of the control signal head has the second radius of curvature at least on the side of the rotary head in the direction perpendicular to this direction, the second radius of curvature being larger than the first radius of curvature. A drum unit is capable of bringing the rotary head and the control signal head into contact with the magnetic tape in an excellent manner with the control signal head embedded. With such a construction, a drum unit which is capable of fairly enhancing the utility of a rotary head type recording/reproducing system is provided.