To provide garbage annihilation machine and garbage annihilation method capable of rapidly decomposing garbage and releasing the same in the form of gas into the atmosphere for the purpose of garbage disposal.

A garbage disposal machine 1 has an agitating vessel 11 which is formed of wall surfaces of a cylindrical shape provided with salient projecting parts on the lower side, has a garbage feeding port, an air intake and an air exit 15 in the upper part and has an openable and closable content takeout door 17 at the end faces of the projecting parts in the lower part, an agitator blade revolving shaft 21 which is arranged at the center of a cylindrical part, plural agitator blades 23 which are fixed by struts 22 to the agitator blade revolving shaft 21, are arranged along the inner side of the cylindrical surface of the agitating vessel 11 and agitate the decomposition bacteria in the agitating vessel and the garbage fed therein, a biaxial screw conveyor 30 which is arranged in a manner as to bring the screw flank in proximity to the inside surfaces of the projecting parts of the agitating vessel 11 and is rotatable in forward and backward direction and a driving means 40.