A bearing unit comprises a cylindrical oil-impregnated bearing, in which a bearing bore to support a turning shaft is formed so as to enable the turning shaft to turn; a bearing holder, in which the oil-impregnated bearing is fixed by an inner bore; a first groove being formed in an axial direction on an inner circumferential surface of the oil-impregnated bearing; and a second groove being formed in an axial direction on at least one of an outer circumferential surface of the oil-impregnated bearing and an inner circumferential surface of the bearing holder. The second groove is formed so as to have a greater depth than that of the first groove. The second groove is also formed so as to have a larger cross section than that of the first groove.