cured product of the composition of the present invention other than the substituted monovalent hydrocarbon group of 1 to 10 carbon atoms containing an epoxy group all of the r 1 groups are preferably alkyl groups or aryl groups and are most preferably methyl groups the average polymerization degree of the component a which is represented by a b 2 u00d7 c 2 is an integer of 8 to 20 and is preferably an integer of 10 to 15 c is an integer of 0 to 5 and is preferably an integer of 0 to 3 because the average polymerization degree of the component a is a low value of not more than 20 the component a is necessarily a low viscosity liquid component with a viscosity at 25 u00b0 c of not more than 100 mpa u00b7 s component b is an optional component and is at least one epoxy group containing organopolysiloxane selected from the group consisting of organopolysiloxanes containing a plurality of epoxy groups represented by general formulas 2 to 9 shown below wherein r represents an unsubstituted or substituted monovalent hydrocarbon group of 1 to 10 carbon atoms that does not contain an epoxy group e represents an epoxy group containing monovalent organic group f.