The present invention provides a novel method of producing a recombinant bacterium for production of a non-natural protein, including: (1) expressing tRNA in a bacterium, which tRNA recognizes UAG codon; (2) expressing an aminoacyl-tRNA synthetase in the bacterium, which aminoacyl-tRNA synthetase acylates the tRNA with a non-natural amino acid or an α-hydroxy acid; (3) (i) introducing a DNA construct into the bacterium, which DNA construct is for expressing, in the absence of a release factor for terminating translation at UAG codon, a function of at least one gene selected from the group consisting of genes each of which loses its function when a gene that codes for the release factor is defective and/or introducing an alteration into said at least one gene in a chromosome of the bacterium, which alteration is for expressing the function of said at least one gene in the absence of the release factor; and (4) causing the gene that codes for the release factor in the bacterium to be defective.