PROBLEM TO BE SOLVED: To provide a treating method of organic waste and a treating apparatus thereof by which even the organic waste having high water content is accelerated in microbial degradation in a state as it is to be made into compost or reduced in volume without drying using heat energy or wind blowing as in a conventional manner and also without mixing agricultural by-product such as saw-dust. SOLUTION: In the method of treating the organic waste hardly permeating oxygen in a stand-still state and hardly causing biological reaction with microorganisms, oxygen is forcibly supplied into the organic waste to elevate the inner temperature of the organic waste to which oxygen is supplied by biological reaction and the biological reaction continues while keeping the elevated temperature to compost the organic waste. The composted organic waste causes exothermic reaction in the presence of oxygen and carbon monoxide to reduce the volume or carbonize the organic waste. COPYRIGHT: (C)2010,JPO&INPIT