To realize the miniaturization of a device, the improvement of a disposal efficiency and the simplification of a transportation work and of a maintenance work in a device for volume decreasing disposal for carrying out the compression of a waste plastic container such as a PET bottle or the like for the decreasing disposal of the volume of the container.

A boring and pre-volume-decreasing disposal part 110 and a regular volume-decreasing disposal part are provided separably from each other. In a hopper, in which waste plastic containers are charged, a roll 112, on the outer peripheral surface of which boring pins are protrusively provided, is rotatably arranged along the bottom plate 111f of the hopper. At the same time, a pre-volume decreasing disposal passage 111A, the space of which gradually becomes narrower from the charging port side to the outlet side of the hopper, is formed between the outer peripheral surface of the roll 112 and the bottom plate 111f. Further, a feeding conveyor 12 for conveying the waste plastic containers discharged from the outlet 111B of the hopper to the charging port of the regular volume decreasing disposal part is provided.