A method including correcting output of an image sensor unit based on correction information of the image sensor unit that captures and discriminates a paper sheet. A apparatus includes an image sensor unit which includes an image capturing element that captures a banknote so as to discriminate the banknote, a controller that controls the image sensor unit, and a first attachment part, to which the image sensor unit is attached to be detachable, and which includes a connection terminal that connects the image sensor unit and the controller with each other, and which is arranged in a conveyance path for conveying the banknote.