A sleeve allows insertion of an oil control valve, and is used by being inserted to an installation hole provided in a cylinder head cover. An outer surface of a sleeve main body of the sleeve is covered by a rubber-like elastic body layer. The rubber-like elastic body layer has a protrusion provided in the periphery of an oil hole provided in the sleeve main body in such a manner as to surround the oil hole. In accordance with the sleeve, it is possible to install the oil control valve to the cylinder head cover at a high oil tightness.