An epoxy resin composition containing: an epoxy resin having an epoxy equivalent of 500 to 10,000 g/eq, as measured in accordance with JIS K7236, and represented by the general formula below: wherein, in the formula, each Ar is independently a structure having an aromatic ring being unsubstituted or having a substituent, X is a structural unit represented by the general formula below, and Y is a structural unit represented by the general formula below: wherein in the formulae and, Ar is the same as above, each of R 1 and R 2 is independently a hydrogen atom, a methyl group, or an ethyl group, R' is a divalent hydrocarbon group having 2 to 12 carbon atoms, each of R 3, R 4, R 7, and R 8 is independently a hydroxyl group, a glycidyl ether group, or a 2-methylglycidyl ether group, each of R 5, R 6, R 9, and R 10 is independently a hydrogen atom or a methyl group, n1 is an integer of 4 to 16, n2 is an average of the number of repeating units, and 2 to 30, each of R 11 and R 12 is independently a glycidyl ether group or a 2-methyl glycidyl ether group, each of R 13 and R 14 is independently a hydroxyl group, a glycidyl ether group, or a 2-methyl glycidyl ether group, R 15 and R 16 are a hydrogen atom or a methyl group, m1, m2, p1, p2, and q are an average of the number of repeating units, each of m1 and m2 is independently 0 to 25, and m1 + m2 ≥ 1, each of p1 and p2 is independently 0 to 5, and q is 0.5 to 5, wherein, a bond between X represented by the general formula above and Y represented by the general formula above is optionally random or block, indicating that the total numbers of the numbers of the structural units X and Y present in one molecule are m1 and m2, respectively; an epoxy resin having an epoxy equivalent of 100 to 300 g/eq, as measured in accordance with JIS K7236; and thermally expandable particles. an epoxy resin having an epoxy equivalent of 500 to 10,000 g/eq, as measured in accordance with JIS K7236, and represented by the general formula below: wherein, in the formula, each Ar is independently a structure having an aromatic ring being unsubstituted or having a substituent, X is a structural unit represented by the general formula below, and Y is a structural unit represented by the general formula below: wherein in the formulae and, Ar is the same as above, each of R 1 and R 2 is independently a hydrogen atom, a methyl group, or an ethyl group, R' is a divalent hydrocarbon group having 2 to 12 carbon atoms, each of R 3, R 4, R 7, and R 8 is independently a hydroxyl group, a glycidyl ether group, or a 2-methylglycidyl ether group, each of R 5, R 6, R 9, and R 10 is independently a hydrogen atom or a methyl group, n1 is an integer of 4 to 16, n2 is an average of the number of repeating units, and 2 to 30, each of R 11 and R 12 is independently a glycidyl ether group or a 2-methyl glycidyl ether group, each of R 13 and R 14 is independently a hydroxyl group, a glycidyl ether group, or a 2-methyl glycidyl ether group, R 15 and R 16 are a hydrogen atom or a methyl group, m1, m2, p1, p2, and q are an average of the number of repeating units, each of m1 and m2 is independently 0 to 25, and m1 + m2 ≥ 1, each of p1 and p2 is independently 0 to 5, and q is 0.5 to 5, wherein, a bond between X represented by the general formula above and Y represented by the general formula above is optionally random or block, indicating that the total numbers of the numbers of the structural units X and Y present in one molecule are m1 and m2, respectively; an epoxy resin having an epoxy equivalent of 100 to 300 g/eq, as measured in accordance with JIS K7236; and thermally expandable particles.