Provided are a thermosetting resin composition comprising an adduct resin (X) that is a reaction product of an amine-epoxy resin (A) and an epoxy modifier (B) described below, and an epoxy resin curing agent (C), wherein the adduct resin (X) is a reaction product obtained by reacting 1 to 20 parts by mass of the epoxy modifier (B) with 100 parts by mass of the amine-epoxy resin (A), and a prepreg, a fiber-reinforced composite material, and a high-pressure gas container in which the thermosetting resin composition is used.
Epoxy modifier (B): at least one selected from the group consisting of meta-xylylenediamine, para-xylylenediamine, 4,4'-diaminodiphenylmethane, and 4,4'-diaminodiphenylsulfone.