Organopolysiloxanes forming the silicon based resins employing in the present invention are preferably comprised of compositions containing organopolysiloxanes represented by an average compositional expression R2a(CnH2n+1)bSiO(4???a???b) (wherein R2 represents a hydrogen atom, a hydroxyl group, an amino group, a halogen atom or an organic group other than alkyl groups, a>0, b>0, 0<a+b<2, and n re