To decompose a large amount of garbage with high efficiency in a short time by constituting a treating chamber of a single chamber, arranging a rotary shaft fixed with a special number of agitation blades in left and right and parallel, stirring and moving the garbage, etc., with the rotation in the mutually reverse directions, and circulating it in a treating tank.

A main body 1 formed in a square box shape is provided with a treating tank 2 of a single chamber and a control chamber therein. Two rotary shafts 4, 5 are arranged parallelly and horizontally in the treating tank 2, and plural agitation blades 6 are erected on respective shafts. A partitioning plate 7 is fitted only to a central part between the rotary shafts 4, 5. The garbage, etc., are stirred and moved in the mutual reverse directions, as shown with arrows, to allow them to circulate in the treating tank 2 and decompose. The treating tank 2 inside is heated with a heater 10 via a blower 11 and a duct 12 and also heat keeping effect is enhanced with a heat insulating material 1a.