To develop a compacting device of the integrated structure of a compression chamber, a press lid, a main cylinder, a gate, an operation unit, etc., with each other.

In a compacting device of a waste car, etc., consisting of a compression process and a discharge process b a main cylinder 7, a pre- compression chamber formed by providing a pre-compression frame 3a on a device body at the position before a gate 8, i.e., between a press lid 4 and the gate 8 in the condition in which the press lid 4 is closed to reduce the compressive reaction applied on the press lid during the compression, and the main cylinder 7 is retracted to an appropriate prescribed position and the gate 8 is opened after the compression to reduce the bearing pressure on the gate 8.