Abstract: Apparatus for comminuting industrial and/or bulky domestic waste materials has an upright housing with a funnel-shaped section located above a stationary counterknife which cooperates with a single rotary knife therebelow or with two rotary knifes respectively disposed thereabove and therebelow. The inner side of the funnel-shaped housing section has a downwardly sloping spiral surface which advances waste material downwardly toward the upper rotary knife or toward the counterknife and whose upper portion flares outwardly and downwardly at a gradually diminishing angle with respect to the common axis of the knives. The lower portion of the spiral surface merges gradually into the upper portion and thereupon flares outwardly and upwardly with respect to the common axis. A feeding device which rotates with the rotary knife or knives extends into the funnel-shaped section and has one or more arms whose edge portions resemble spirals or helices having a lead opposite to that of the spiral surface.