To provide a medium processor suitable for miniaturization, capable of preventing simultaneous insertion of a plurality of media without destroying a medium.

In a bill processor 1 as this medium processor, a swing member 510 preventing the simultaneous insertion of bills P as the media is formed deformably by abutment on the bill P. As a result, even if a first end part 510a abuts on the bill by swing operation accompanying the abutment between a second end part 510b of the swing member 510 and the bill P, the first end part 510a itself is deformed to relax a shock to the bill P, so that the destruction of the bill P is not caused. Accordingly, it is not necessary to set a distance between the first end part 510a and the second end part 510b to a length of a conveyance direction of the bill P or above so as to prevent the destruction of the bill P, and the distance between the first end part 510a and the second end part 510b is shortened to miniaturize not only the swing member 510 but also the whole processor 1.