A resin composition, comprising: epoxy resin; a curing agent; and vinyl polymer particles, wherein the content of epoxy resin with a weight average_molecular weight of 100 to 480 is set at 30 to 90 parts by mass in 100 parts by mass of the epoxy resin, the content of epoxy resin with a weight average molecular weight of 2000 to 40000 is set at 10 to 70 parts by mass in 100 parts by mass of the epoxy resin, and wherein the molecular weights are determined using the GPC method described in the present description, wherein the vinyl polymer particles are obtained by conducting two or more stages of emulsion polymerization on vinyl monomer mixtures having different compositions, and by spray-drying the emulsion of the vinyl polymer, the content of the vinyl polymer particles is set at 2 to 30 parts by mass per 100 parts by mass of the epoxy resin, and the maximum value of instantaneous increase in viscosity of the vinyl polymer particles is set at 0.3 to 5.0 Pa·s/°C which is determined by the following method: preparing a sample resin composition by mixing 100 parts by mass of bisphenol-A epoxy resin with an epoxy equivalent weight of 184 to 194 g/eq. and 10 parts by mass of the vinyl polymer particles, measuring the viscosity of the prepared sample resin composition by a rheometer, using a 25 mm-diameter parallel plate under conditions of plate gap: 0.5 mm, frequency: 10 rad/sec., rate of temperature rise: 2°C/min., measuring interval: 30 sec., starting measurement temperature: 30°C and stress: 300 Pa, obtaining the instantaneous increase in viscosity base on An+1=(Vn+1-Vn) / (Tn+1-Tn), herein Tn+1 (°C) and Vn+1 (Pa·s) are the temperature and viscosity at the (n+1)th measurement, and Tn (°C) and Vn (Pa·s) are the temperature and viscosity at the (n)th measurement, and describing the maximum value of "An+1" as the maximum value of instantaneous increase in viscosity. epoxy resin; a curing agent; and vinyl polymer particles, wherein the content of epoxy resin with a weight average_molecular weight of 100 to 480 is set at 30 to 90 parts by mass in 100 parts by mass of the epoxy resin, the content of epoxy resin with a weight average molecular weight of 2000 to 40000 is set at 10 to 70 parts by mass in 100 parts by mass of the epoxy resin, and wherein the molecular weights are determined using the GPC method described in the present description, wherein the vinyl polymer particles are obtained by conducting two or more stages of emulsion polymerization on vinyl monomer mixtures having different compositions, and by spray-drying the emulsion of the vinyl polymer, the content of the vinyl polymer particles is set at 2 to 30 parts by mass per 100 parts by mass of the epoxy resin, and the maximum value of instantaneous increase in viscosity of the vinyl polymer particles is set at 0.3 to 5.0 Pa·s/°C which is determined by the following method: preparing a sample resin composition by mixing 100 parts by mass of bisphenol-A epoxy resin with an epoxy equivalent weight of 184 to 194 g/eq. and 10 parts by mass of the vinyl polymer particles, measuring the viscosity of the prepared sample resin composition by a rheometer, using a 25 mm-diameter parallel plate under conditions of plate gap: 0.5 mm, frequency: 10 rad/sec., rate of temperature rise: 2°C/min., measuring interval: 30 sec., starting measurement temperature: 30°C and stress: 300 Pa, obtaining the instantaneous increase in viscosity base on An+1=(Vn+1-Vn) / (Tn+1-Tn), herein Tn+1 (°C) and Vn+1 (Pa·s) are the temperature and viscosity at the (n+1)th measurement, and Tn (°C) and Vn (Pa·s) are the temperature and viscosity at the (n)th measurement, and describing the maximum value of "An+1" as the maximum value of instantaneous increase in viscosity. preparing a sample resin composition by mixing 100 parts by mass of bisphenol-A epoxy resin with an epoxy equivalent weight of 184 to 194 g/eq. and 10 parts by mass of the vinyl polymer particles, measuring the viscosity of the prepared sample resin composition by a rheometer, using a 25 mm-diameter parallel plate under conditions of plate gap: 0.5 mm, frequency: 10 rad/sec., rate of temperature rise: 2°C/min., measuring interval: 30 sec., starting measurement temperature: 30°C and stress: 300 Pa, obtaining the instantaneous increase in viscosity base on An+1=(Vn+1-Vn) / (Tn+1-Tn), herein Tn+1 (°C) and Vn+1 (Pa·s) are the temperature and viscosity at the (n+1)th measurement, and Tn (°C) and Vn (Pa·s) are the temperature and viscosity at the (n)th measurement, and describing the maximum value of "An+1" as the maximum value of instantaneous increase in viscosity.