To provide a simple and compact volume reduction device for PET bottles or the like capable of remarkably reducing the volume of PET bottles or the like by man power.

The device is composed of: a pressure receiving means having a pressure receiving member which is a sheet material having a planar shape and bent into a circular-arc shape in the longitudinal direction for storing PET bottles, and at one end of which an end plate for locking the PET bottles is fixed in the longitudinal direction; and a pressing means provided with a roller capable of performing pendulum movements while holding prescribed spacing with the pressure receiving member and also freely capable of rotating for grinding down the PET bottles. The volume of the PET bottles stored into the pressure receiving means is reduced while they are ground down by the pendulum operation of the pressing means.