A resin composition including: a thermosetting resin component including a mesogen; and a phosphorus atom-containing thermoplastic polymer type frame retardant, wherein the thermoplastic polymer type frame retardant is a phosphorous atom-containing formed by polymerizing or copolymerizing one of monomers represented by general formulae (1) and (2) below, wherein, in the general formulae (1) and (2), each of R1 and R2 is any one of an alkyl group, an alkoxy group, an aryl group and an aryloxy group, R1 and R2 being different or identical, and R3 is a methyl group or a hydrogen atom.