Abstract: The present invention relates to an apparatus that achieves improvements in weight recovery ratio and processing capability in the separation of a protein-rich component from brewer's spent grain (BSG), without reducing the protein content in the protein-rich product, and thus makes it possible to reuse BSG as an inexpensive, but superior, protein-rich resource. Brewer's spent grain in a wet state is supplied to a roll mill having a pair of rolls provided with cutting edges and rotating at a predetermined rotational speed ratio, whereby the protein-rich product of the BSG is crushed and peeled from the husk component.