To provide the volume reducing treatment device for resin vessels, which has a simple structure, no waiting time for charging the resin vessel and a short volume reducing treatment time.

When a drum 1 is rotated under the condition that a resin vessel 8 is placed at a position (a), since the interval between the drum 1 and a guide block 3 is narrowed together with the rotation of the drum, the charged resin vessel 8 is fed towards a position (b) and compressed, then further compression-deformed and finally discharged at a position (a). When a load applying to the guide block 3 becomes larger in accompany with the compression of the resin vessel 8, springs 6, which supports the guide block 3, are compressed, resulting in widening the intervals between the drum 1 and the guide block 3 and consequently preventing an overload from applying to a motor.