THE PRESENT INVENTION PROVIDES A METHOD OF TREATING BIOMASS THAT REDUCES WATER-POLLUTING SUBSTANCES, SUPPRESSES THE PRODUCTION OF MALODOROUS GASES AND GREENHOUSE GASES, DECREASES THE NITROGEN CONTENT IN THE COMPOST OR LIVESTOCK BEDDING THUS PREPARED, AND FURTHERMORE, EASILY TREATS NITROGEN-CONTAINING BIOMASS IN A SHORT TIME AT HIGH TEMPERATURE. THE PRESENT INVENTION ALSO PROVIDES COMPOST AND LIVESTOCK BEDDING PRODUCED BY THE METHOD AND A BIOMASS TREATING AGENT. THE METHOD OF TREATING BIOMASS INCLUDES BLENDING, WITH NITROGEN-CONTAINING BIOMASS, A GEOBACILLUS MICROORGANISM HAVING DENITRIFICATION CAPABILITY AND A FERMENTATION PROMOTER THAT PROMOTES THE FERMENTATION OF THE NITROGEN-CONTAINING BIOMASS BY THE GEOBACILLUS MICROORGANISM.
