Epoxy resin composition, resin cured product, fiber-reinforced composite material, and prepreg

A prepreg comprising an epoxy resin composition and reinforcing fibers, wherein

• the epoxy resin composition comprises
• 80% or more by mass of an epoxy resin (A), which is a glycidyl ether-type epoxy resin,
• a polyrotaxane (B) having graft-chain-modified cyclic molecules, the graft chain of which is an aliphatic polyester,
• at least one crosslinking agent (C) selected from the group consisting of a polyisocyanate compound and a polyol compound, and capable of reacting with the polyrotaxane,
• wherein the total content ratio of the polyrotaxane (B) and the at least one crosslinking agent (C) is 1% by mass or more and less than 10% by mass relative to the whole amount of the epoxy resin composition, wherein the ratio of the polyrotaxane (B) relative to the total amount of the polyrotaxane (B) and the at least one crosslinking agent (C) is 20% by mass or more and less than 70% by mass, and
• a curing agent (D) capable of reacting with the epoxy resin (A), which is an amine-type curing agent;
• and
• wherein the reinforcing fibers are carbon fibers which are arranged in one direction.