A sensing device including: a sensing section having an illuminating section that illuminates light and a light-receiving section that receives reflected light of light illuminated from the illuminating section, the sensing section sensing an image on a recording medium; a housing that accommodates the illuminating section; a covering member covering the housing, that is freely installed at and removed from the housing, having a transmitting member through which the light from the illuminating section is transmitted; and a setting section disposed at an opposite side to a housing side with respect to the covering member, the setting section being freely installed at and removed from the housing, and having a setting surface that sets a position at which the recording medium reflects light, wherein, at a positioning portion of the setting section, the covering member is positioned at least in a direction perpendicular to the setting surface, is provided.