PCT No. PCT/FI84/00083 Sec. 371 Date Jul. 2, 1985 Sec. 102(e) Date Jul. 2, 1985 PCT Filed Nov. 16, 1984 PCT Pub. No. WO85/02172 PCT Pub. Date May 23, 1985.Apparatus for treating waste, particularly household waste, by means of composting. The waste is collected in a generally known fashion into the collecting bowl (1), wherefrom they are immediately moved on the spiral conveyor (21) into the mixing drum (5), which is set into rotating motion by means of the actuator (12). Inside the mixing drum (5) there is arranged an amount of such medium substance which is formed of separate plastic or steel bullets, onto the surface whereof the waste sticks during mixing. In connection to the mixing drum (5) there is arranged the discharge space (9), which is provided with separator means (10) for separating the composted waste or soil. The compost soil is continuously moved out of the discharge space (9) and further into a bag or the equivalent. A partial feedback of the soil is arranged from the discharge space (9) back into the collecting bowl.