(A) A reinforcing fiber, (B) a resin particle, and (C) a matrix resin are combined to prepare a resin composition which improves a reinforcing effect by the reinforcing fiber. The reinforcing fiber (A) contains a carbon fiber. The resin particle (B) contains a semicrystalline thermoplastic resin, the semicrystalline thermoplastic resin in the resin particle (B) has an exothermic peak in a temperature range between a glass transition temperature of the semicrystalline thermoplastic resin and a melting point of the semicrystalline thermoplastic resin, the peak being determined by heating the resin particle (B) at a rate of 10° C./min. by differential scanning calorimetry (DSC), and the resin particle (B) has an average particle size of 3 to 40 μm. The semicrystalline thermoplastic resin may be a polyamide resin having a melting point of not lower than 150° C. (particularly, a polyamide resin having an alicyclic structure and a glass transition temperature of not lower than 100° C., or a polyamide resin having a γ-type crystal structure or a degree of crystallinity of not more than 50%). The matrix resin (C) may be a thermosetting resin.