To provide a volume reducing apparatus for a container for preventing occurrence of a situation that the volume of the container is reduced together with a metal cap by securely detecting presence or absence of the cap in the container.

The volume reducing apparatus for a container comprises an apparatus body 1 having an inlet 3 for introducing the container P from which its content is removed therein, a container support 11 provided at the inlet of the body to place the container to be introduced from the inlet, a metal sensor 20 provided at the support to detect a metal cap mounted at a neck of the container, a container retaining means 22 provided at the support to move the container placed on the support to a position where its neck is brought into contact with a metal sensor and to retain it, a volume reducing means provided at the body to volume reduce the container introduced from a container receiver, and a container recovery unit provided at the body to receive the container volume reduced by the reducing means.