The present invention provides a mutant Bacillus bacterium capable of enhancing productivity of proteins or polypeptides, a recombinant microorganism produced by introducing genes encoding heterologous proteins or polypeptides into the mutant Bacillus bacterium, and a method for producing proteins or polypeptides by use of the recombinant microorganism.A mutant Bacillus bacterium which has, on the genome or plasmid thereof, DNA having a promoter sequence which is recognized and transcribed specifically during the sporulation stage and which is ligated to an upstream end of a sigA gene or a gene equivalent thereto, a recombinant microorganism produced by introducing genes encoding heterologous proteins or polypeptides into the mutant Bacillus bacterium, and a method for producing proteins or polypeptides by use of the recombinant microorganism.