An epoxy resin composition comprising component, which is an epoxy resin, component, which is dicyandiamide, component, which is aromatic urea, and component, which is a boric ester, and fulfilling any of the conditions from (i) to (iii) given below: (i) to meet requirement [a] and requirement [b] and component contains a tri-or higher polyfunctional epoxy resin, (ii) to meet requirement [c] and requirement [d], and (iii) to meet requirement [c] and requirement [e], where requirements [a] to [e] are as follows: [a]: the time period after reaching 100°C until reaching the peak top in the heat flow curve is 60 minutes or shorter when an epoxy resin composition is analyzed in an nitrogen stream at a constant temperature of 100°C using a differential scanning calorimeter, [b]: the time period after reaching 60°C until reaching the peak top in the heat flow curve is 25 hours or longer when an epoxy resin composition is analyzed in an nitrogen stream at a constant temperature of 60°C using a differential scanning calorimeter, [c]: the average epoxy equivalent over all epoxy resins is 165 g/eq or more and 265 g/eq or less, [d]: component contains an epoxy resin that is represented by formula and/or formula and accounts for 10 parts by mass to 50 parts by mass of the total epoxy resin quantity, which represents 100 parts by mass: wherein R 1, R 2, and R 3 each are a hydrogen atom or a methyl group, and n is an integer of 1 or greater, wherein n is an integer of 1 or greater, and [e]: component contains a tri- or higher functional glycidyl amine type epoxy resin that accounts for 10 parts by mass to 50 parts by mass of the total epoxy resin quantity, which represents 100 parts by mass. (i) to meet requirement [a] and requirement [b] and component contains a tri-or higher polyfunctional epoxy resin, (ii) to meet requirement [c] and requirement [d], and (iii) to meet requirement [c] and requirement [e], where requirements [a] to [e] are as follows: [a]: the time period after reaching 100°C until reaching the peak top in the heat flow curve is 60 minutes or shorter when an epoxy resin composition is analyzed in an nitrogen stream at a constant temperature of 100°C using a differential scanning calorimeter, [b]: the time period after reaching 60°C until reaching the peak top in the heat flow curve is 25 hours or longer when an epoxy resin composition is analyzed in an nitrogen stream at a constant temperature of 60°C using a differential scanning calorimeter, [c]: the average epoxy equivalent over all epoxy resins is 165 g/eq or more and 265 g/eq or less, [d]: component contains an epoxy resin that is represented by formula and/or formula and accounts for 10 parts by mass to 50 parts by mass of the total epoxy resin quantity, which represents 100 parts by mass: wherein R 1, R 2, and R 3 each are a hydrogen atom or a methyl group, and n is an integer of 1 or greater, wherein n is an integer of 1 or greater, and [e]: component contains a tri- or higher functional glycidyl amine type epoxy resin that accounts for 10 parts by mass to 50 parts by mass of the total epoxy resin quantity, which represents 100 parts by mass. [a]: the time period after reaching 100°C until reaching the peak top in the heat flow curve is 60 minutes or shorter when an epoxy resin composition is analyzed in an nitrogen stream at a constant temperature of 100°C using a differential scanning calorimeter, [b]: the time period after reaching 60°C until reaching the peak top in the heat flow curve is 25 hours or longer when an epoxy resin composition is analyzed in an nitrogen stream at a constant temperature of 60°C using a differential scanning calorimeter, [c]: the average epoxy equivalent over all epoxy resins is 165 g/eq or more and 265 g/eq or less, [d]: component contains an epoxy resin that is represented by formula and/or formula and accounts for 10 parts by mass to 50 parts by mass of the total epoxy resin quantity, which represents 100 parts by mass: wherein R 1, R 2, and R 3 each are a hydrogen atom or a methyl group, and n is an integer of 1 or greater, wherein n is an integer of 1 or greater, and [e]: component contains a tri- or higher functional glycidyl amine type epoxy resin that accounts for 10 parts by mass to 50 parts by mass of the total epoxy resin quantity, which represents 100 parts by mass.