Waste compacting unit comprising: - at least one inlet (103a,103b) for introducing a waste to treat; - a compacting chamber; - waste compacting means acting in said compacting chamber, said waste compacting means being mounted on a carriage; - a resiliently yieldable wall comprising an interposition plate arranged in said compacting chamber, said waste compacting means arranged to compact said waste against the resiliently yieldable wall comprising said interposition plate; - motor driven means (22,50)arranged to cause the waste compacting means and the carriage to move along a working direction; - piercing means provided in said compacting chamber and arranged to cooperate with said compacting means to cause a volume reduction of said waste, said piercing means comprising a plurality of piercing elements arranged to pierce said waste during a compacting step operated by said waste compacting means; - means for extracting the compacted waste from said piercing elements, the means for extracting being provided in said compacting chamber; - at least one compacted waste collecting bin (35a,35b) arranged below said compacting chamber, said compacting chamber having a base comprising at least one portion (4a,4b) movable between a supporting position, where the base (4a,4b) is closed and prevents an access towards said waste collecting bin (35a,35b), and a releasing position, where the base (4a,4b) is opened and allows an access towards said waste collecting bin (35a,35b); - said means for extracting comprises the interposition plate positioned between a side wall and a respective portion of said compacting chamber, said interposition plate being provided with apertures arranged to be crossed by said piercing elements and being capable of translating, biased by resilient means, towards/away from the side walls for respectively uncovering/covering said piercing elements; said waste compacting unit being characterized in that each portion of said base (4a,4b) has engaging/releasing means arranged to keep each portion of said base (4a,4b) in the supporting position or in the releasing position respectively, said engaging/releasing means comprising at least one protruding side wall integral to said base (4a,4b) suitable for engaging/releasing in/from a groove made in said interposition plate; and in that the movement of said base (4a,4b) between said supporting position and said releasing position is directly operated by said carriage. - at least one inlet (103a,103b) for introducing a waste to treat; - a compacting chamber; - waste compacting means acting in said compacting chamber, said waste compacting means being mounted on a carriage; - a resiliently yieldable wall comprising an interposition plate arranged in said compacting chamber, said waste compacting means arranged to compact said waste against the resiliently yieldable wall comprising said interposition plate; - motor driven means (22,50)arranged to cause the waste compacting means and the carriage to move along a working direction; - piercing means provided in said compacting chamber and arranged to cooperate with said compacting means to cause a volume reduction of said waste, said piercing means comprising a plurality of piercing elements arranged to pierce said waste during a compacting step operated by said waste compacting means; - means for extracting the compacted waste from said piercing elements, the means for extracting being provided in said compacting chamber; - at least one compacted waste collecting bin (35a,35b) arranged below said compacting chamber, said compacting chamber having a base comprising at least one portion (4a,4b) movable between a supporting position, where the base (4a,4b) is closed and prevents an access towards said waste collecting bin (35a,35b), and a releasing position, where the base (4a,4b) is opened and allows an access towards said waste collecting bin (35a,35b); - said means for extracting comprises the interposition plate positioned between a side wall and a respective portion of said compacting chamber, said interposition plate being provided with apertures arranged to be crossed by said piercing elements and being capable of translating, biased by resilient means, towards/away from the side walls for respectively uncovering/covering said piercing elements;