A resin composition comprising: a silicone resin containing a constitutional unit shown by the following composition formula and having a weight average molecular weight of 3,000 to 500,000, wherein R 1 to R 4 each independently represent a monovalent hydrocarbon group having 1 to 8 carbon atoms, with the proviso that the both of R 3 and R 4 are not methyl groups at the same time; "m" and "n" are each independently an integer of 0 to 300; the both of "a" and "b" are positive numbers satisfying a+b = 1; each of "X" independently represents a divalent linking group shown by the following general formula or a divalent linking group shown by the following general formula, with the proviso that part of or all of the "X" in the formula are divalent linking group(s) shown by the following general formula, and when the molar number of a unit shown by the following general formula is defined as "c", and the molar number of a unit shown by the following general formula is defined as "d", a ratio between the "c" and the "d" is in a range of 0≤d≤1 when the "c" is assumed to be 1; wherein R 5 represents a hydrogen atom or a methyl group, and "p" is an integer of 0 to 7; wherein R 6 represents a hydrogen atom or a methyl group, R 7 and R 8 each independently represent a monovalent hydrocarbon group having 1 to 8 carbon atoms, with the proviso that the both of R 7 and R 8 are not methyl groups at the same time, "q" and "r" are each independently an integer of 0 to 300, and "k" is an integer of 0 to 7; an epoxy resin-curing agent; and a filler; wherein the mass fraction of the component is 50 to 95% by mass based on the total mass. a silicone resin containing a constitutional unit shown by the following composition formula and having a weight average molecular weight of 3,000 to 500,000, wherein R 1 to R 4 each independently represent a monovalent hydrocarbon group having 1 to 8 carbon atoms, with the proviso that the both of R 3 and R 4 are not methyl groups at the same time; "m" and "n" are each independently an integer of 0 to 300; the both of "a" and "b" are positive numbers satisfying a+b = 1; each of "X" independently represents a divalent linking group shown by the following general formula or a divalent linking group shown by the following general formula, with the proviso that part of or all of the "X" in the formula are divalent linking group(s) shown by the following general formula, and when the molar number of a unit shown by the following general formula is defined as "c", and the molar number of a unit shown by the following general formula is defined as "d", a ratio between the "c" and the "d" is in a range of 0≤d≤1 when the "c" is assumed to be 1; wherein R 5 represents a hydrogen atom or a methyl group, and "p" is an integer of 0 to 7; wherein R 6 represents a hydrogen atom or a methyl group, R 7 and R 8 each independently represent a monovalent hydrocarbon group having 1 to 8 carbon atoms, with the proviso that the both of R 7 and R 8 are not methyl groups at the same time, "q" and "r" are each independently an integer of 0 to 300, and "k" is an integer of 0 to 7; an epoxy resin-curing agent; and a filler; wherein the mass fraction of the component is 50 to 95% by mass based on the total mass.