To enhance abrasion resistance of compositional members by forming at least a part of a head of a hybrid material where organic and inorganic materials are mixed through molecular bond.

At least a part of a head is formed of a hybrid material where organic and inorganic materials are mixed through molecular bond. The hybrid material is composed of a resin having a skeletal of polyimide with an inorganic material bonded to the side chain thereof. Oxygen in the imide group of polyimide is linked with the end OH group of the inorganic material SiO2 through hydrogen bond and coordination hybridized. More specifically, the molecule SX of inorganic material is bonded to the skeletal PI of polyimide molecule as a side chain through a hydrogen bonding part B. Because of such a bond, dispersion level is on the order of nm(1×19-9 m) and the inorganic material is not removed easily nor missed through abrasion.