Disclosed are bridged nucleosides and nucleotides. The nucleosides of the present invention have a 2′,4′-bridged structure and are represented by formula I below: An oligonucleotide containing a 2′,4′-bridged artificial nucleotide of the present invention has a binding affinity for single-stranded RNA comparable to that of known 2′,4′-BNA/LNA and higher nuclease resistance than LNA. In particular, since the oligonucleotide has a much higher binding affinity for single-stranded RNA than S-oligo, it is expected that the oligonucleotide is applicable to nucleic acid drugs.