Provided are a mRNA that forcibly expresses a protein gene in response to a miRNA, and a method for forcibly expressing the same. This artificial mRNA comprises: a sequence that encodes a protein gene; a miRNA target sequence connected to the 3' side of a PolyA sequence; and a translation repression sequence connected to the 3' side of the miRNA target sequence. Also disclosed is a method for expressing a protein gene in response to the expression of a miRNA, the method comprising a step for introducing said artificial mRNA into a cell.