Paper sheets preprocessing apparatus includes a material remover, a detector, a controller, and a display. The material remover removes a material from a paper sheets assembly. The paper sheets assembly includes a plurality of paper sheets strapped by the material. The detector is located at an upstream side than the material remover, and detects information of the paper sheets assembly. The controller decides whether the paper sheets assembly satisfies a predetermined specification, based on the information detected by the detector. If the controller decides that the paper sheets assembly does not satisfy the predetermined specification, the display displays a reason to decide that the paper sheets assembly does not satisfy the predetermined specification.