To provide a waste disposer which recovers a rare earth/boron/ ferropermanent magnet from the waste containing the rare earth/boron/ ferropermanent magnet recently used as a permanent magnet, as a constituent part.

A metal mass freezing and crushing device 1a of the waste disposer comprises a hydrogen concentration sensor 15 for detecting a hydrogen concentration, a hydrogen atmosphere forming device 2 which is of a hermetically sealed structure with an inlet and an outlet shutter 10 and 11 and filled internally with hydrogen after receiving the carried-in metal mass, a cooling device 3 which cools the carried-out metal mass from the hydrogen atmosphere forming device 2 at a temp. not higher than -100°C, a crusher 4 for crushing the metal mass carried out of the cooling device 3 and a sieving magnetic selector 5 which selects the rare earth/boron/ferropermanent magnet from the metal mass crushed by the crusher 4.