According to the present disclosure, a reading module includes a light source, an optical system, and a sensor. The optical system images, as image light, reflection light of light with which the light source has irradiated a document. The sensor converts the thus imaged image light into an electric signal. The optical system includes a mirror array in which a plurality of reflection mirrors are connected together, and a plurality of aperture stop portions. The reflection mirrors each reflect light at an angle that is different, as seen in a main scanning direction, from an angle at which an adjacent one of the reflection mirrors reflects light. The plurality of aperture stop portions are disposed on one side of the mirror array with respect to an orthogonal direction which is orthogonal to the main scanning direction.