An mRNA forcibly expresses a protein gene in response to a miRNA, and a method for forcibly expressing the same, are provided. An artificial mRNA comprising a sequence encoding a protein gene, a miRNA target sequence linked to the 3′-terminal side of a Poly A sequence, and a translational repression sequence linked to the 3′-terminal side of the miRNA target sequence; and a method for expressing a protein gene in response to the expression of a miRNA, comprising a step of introducing the artificial mRNA into a cell.