To provide a shredder which is manufactured at a low cost since the shredder is constituted of a simple structure and is conveniently used by having the shredder readily at home.

The purpose of the invention is achieved by the shredder which consists of two planar plates, has protrusions and/or recessed parts on one planar plate, has recessed parts corresponding to positions, the number, a size, and a cross-sectional shape of the protrusions of one planar plate and/or protrusions corresponding to positions, the number, a size, and a shape of the recessed parts of one planar plate on the other planar plate, and is characterized by a total area of the recessed parts which is at least 10% of a target area.