The present invention addresses the problem of providing a method for acquiring Bacillus subtilis var. natto which has a markedly low sporulation capacity upon fermenting soybeans and using this bacterium to produce natto with a low content of Bacillus subtilis var. natto spores using existing equipment and processes without the problems of fermentation failures and bacterial contamination. The present invention provides a mutant strain of Bacillus subtilis var. natto that, relative to a sporulation capacity of 100% in a culture medium comprising at least 200 μg/ml of dipicolinic acid, has a sporulation capacity of no higher than 5% in a culture medium that does not include dipicolinic acid, and has the quality of being able to produce natto which has excellent filament formation and appearance. The present invention also provides natto produced using said mutant strain, and a natto production method using said mutant strain.
