To perform appropriate pH adjustment to the raising environment of microorganisms in a garbage treating device in which the decomposition treatment of the garbage is performed by microorganisms.

To a microorganism decomposition part 11 wherein garbage is subjected to decomposition treatment by a microorganism carrier 12 on which high temperature microorganisms are carried, alkali metal hydrogen carbonate (potassium hydrogen carbonate) is added. And to the microorganism decomposing part 11, a neutralizer (potassium carbonate) reacted with organic acid generated by garbage decomposition by microorganisms to form salts of the organic acid is added. In this way, even when material of low pH such as cedar chips is used as the microorganism carrier, the pH of the microorganism carrier 12 is quickly transferred to an alkali area, and it can be maintained in the pH range which is raising conditions of the microorganisms.