PROBLEM TO BE SOLVED: To provide a decomposing agent, which is capable of completely decomposing garbage to generate no malodor (a deodorizing device is dispensed with) in the decomposition of the garbage by microorganisms. SOLUTION: The decomposing agent for garbage disposal is prepared by mixing a decomposing agent obtained by fermenting a base material having rice bran as a principal component, into which rice hulls, bone phosphorus, fish meal and rape cake are added, with useful microorganisms having aerobic bacteria in harmony with anaerobic bacteria with a fermentation accelerating/ moisture control agent obtained by drying beans and grains.