An epoxy resin composition comprising an epoxy resin and an acid-modified polyolefin resin, the epoxy resin being represented by the formula: wherein X ring is a saturated hydrocarbon ring or an unsaturated hydrocarbon ring, or rings having a structure in which 2 to 6 saturated hydrocarbon rings and/or unsaturated hydrocarbon rings are condensed, or in which 2 saturated hydrocarbon rings and/or unsaturated hydrocarbon rings are connected; R Xa, R Xb, R Xc, and R Xd are the same or different, and each is a hydrogen atom, a lower alkyl group, a lower alkoxy group, a lower alkenyl group, a halogen atom, or a group represented by the formula: wherein R 1 is the same or different, and is a C 1-18 alkyl group, a C 2-9 alkenyl group, a cycloalkyl group, an aryl group, or an aralkyl group, wherein one or more carbon atoms of these groups may be replaced by at least one atom selected from the group consisting of an oxygen atom and a nitrogen atom; R 2 is a C 1-18 alkylene group, wherein one or more carbon atoms of this group other than a carbon atom directly bonded to a silicon atom may be replaced by at least one atom selected from the group consisting of an oxygen atom and a nitrogen atom; R 3 is the same or different, and is a C 1-18 alkyl group, a C 2-9 alkenyl group, a cycloalkyl group, an aryl group, or an aralkyl group, wherein one or more carbon atoms of these groups may be replaced by at least one atom selected from the group consisting of an oxygen atom and a nitrogen atom; m is an integer of 0 to 6; and n is an integer of 0 to 3; provided that at least one of R Xa, R Xb, R Xc, and R Xd is a group represented by the formula; and one or more hydrogen atoms bonded to one or more carbon atoms that constitute the hydrocarbon ring constituting the X ring, and that are not bonded to R Xa, R Xb, R Xc, or R Xd, may be replaced by a lower alkyl group, a lower alkoxy group, a lower alkenyl group, or a halogen atom. wherein X ring is a saturated hydrocarbon ring or an unsaturated hydrocarbon ring, or rings having a structure in which 2 to 6 saturated hydrocarbon rings and/or unsaturated hydrocarbon rings are condensed, or in which 2 saturated hydrocarbon rings and/or unsaturated hydrocarbon rings are connected; R Xa, R Xb, R Xc, and R Xd are the same or different, and each is a hydrogen atom, a lower alkyl group, a lower alkoxy group, a lower alkenyl group, a halogen atom, or a group represented by the formula: wherein R 1 is the same or different, and is a C 1-18 alkyl group, a C 2-9 alkenyl group, a cycloalkyl group, an aryl group, or an aralkyl group, wherein one or more carbon atoms of these groups may be replaced by at least one atom selected from the group consisting of an oxygen atom and a nitrogen atom; R 2 is a C 1-18 alkylene group, wherein one or more carbon atoms of this group other than a carbon atom directly bonded to a silicon atom may be replaced by at least one atom selected from the group consisting of an oxygen atom and a nitrogen atom; R 3 is the same or different, and is a C 1-18 alkyl group, a C 2-9 alkenyl group, a cycloalkyl group, an aryl group, or an aralkyl group, wherein one or more carbon atoms of these groups may be replaced by at least one atom selected from the group consisting of an oxygen atom and a nitrogen atom; m is an integer of 0 to 6; and n is an integer of 0 to 3; provided that at least one of R Xa, R Xb, R Xc, and R Xd is a group represented by the formula; and one or more hydrogen atoms bonded to one or more carbon atoms that constitute the hydrocarbon ring constituting the X ring, and that are not bonded to R Xa, R Xb, R Xc, or R Xd, may be replaced by a lower alkyl group, a lower alkoxy group, a lower alkenyl group, or a halogen atom.