An RNA of the present invention is an RNA containing a 5′ cap structure and a coding region having a 5′ initiation codon and a 3′ stop codon on both ends of the coding region, the RNA having a nucleoside compound introduced at a site selected from among the 5′ cap structure and 10 bases from a 5′ end of the RNA, wherein the nucleoside compound is such that a group is attached to (i) a carbon atom at position 8 of a purine nucleus or (ii) a carbon atom at position 5 or 6 of a pyrimidine nucleus, the group being represented by formula (I): A-X═X-#  (I) where A represents an aryl group or a heteroaryl group, # represents a site where the group represented by the formula (I) is attached to the carbon atom at the position 8 of the purine nucleus or the carbon atom at the position 5 or 6 of the pyrimidine nucleus, and two Xs, which are identical to or different from each other, each represents a nitrogen atom or CH whose H may be substituted by alkyl.