A subgenomic replicon RNA (nucleic acid) having an excellent autonomously replicating ability and a fullgenomic replicon RNA (nucleic acid) having an excellent autonomously replicating ability and infectious HCV particle-producing ability, each derived from a novel HCV of genotype 1b, are provided. Particularly, a subgenomic replicon RNA (nucleic acid) and a fullgenomic replicon RNA (nucleic acid), each derived from an HCV genome of the NC1strain which is a novel HCV genotype 1b isolated from a patient with acute severe hepatitis C, are provided.