A reading module comprising: a light source which radiates light to a document; an optical system which images, as image light (d), light that has been radiated from the light source to the document and reflected from the document; and a sensor in which a plurality of imaging regions (41a, 41b) for converting the image light (d) imaged by the optical system into an electrical signal are arranged next to each other in a main scanning direction, wherein the optical system comprises: a mirror array in which a plurality of reflection mirrors (35a, 35b, 35c) whose reflection surfaces are aspherical concave surfaces are coupled together in an array in the main scanning direction; and a plurality of aperture stop portions each having: a first aperture which adjusts an amount of the image light (d) reflected from the reflection mirror (35a, 35b, 35c); and a second aperture formed between a mirror array and the first aperture, the second aperture shielding stray light that enters the first aperture from an adjacent reflection mirror (35a, 35b, 35c), the first aperture and the second aperture being provided in an optical path of the image light (d) between a reflection mirror (35a, 35b, 35c) and an imaging region (41a, 41b) of the sensor; and between the first aperture and the second aperture, a reflection reduction mechanism (S, 70, 71, 37d) is provided that reduces reflection, toward the first aperture, of light other than the image light (d) traveling from the second aperture to the first aperture, wherein the first aperture and the second aperture are openings provided in an aperture stop main body on a sensor side and on the mirror array side thereof respectively. a light source which radiates light to a document; an optical system which images, as image light (d), light that has been radiated from the light source to the document and reflected from the document; and a sensor in which a plurality of imaging regions (41a, 41b) for converting the image light (d) imaged by the optical system into an electrical signal are arranged next to each other in a main scanning direction, wherein the optical system comprises: a mirror array in which a plurality of reflection mirrors (35a, 35b, 35c) whose reflection surfaces are aspherical concave surfaces are coupled together in an array in the main scanning direction; and a plurality of aperture stop portions each having: a first aperture which adjusts an amount of the image light (d) reflected from the reflection mirror (35a, 35b, 35c); and a second aperture formed between a mirror array and the first aperture, the second aperture shielding stray light that enters the first aperture from an adjacent reflection mirror (35a, 35b, 35c), the first aperture and the second aperture being provided in an optical path of the image light (d) between a reflection mirror (35a, 35b, 35c) and an imaging region (41a, 41b) of the sensor; and a mirror array in which a plurality of reflection mirrors (35a, 35b, 35c) whose reflection surfaces are aspherical concave surfaces are coupled together in an array in the main scanning direction; and a plurality of aperture stop portions each having: a first aperture which adjusts an amount of the image light (d) reflected from the reflection mirror (35a, 35b, 35c); and a second aperture formed between a mirror array and the first aperture, the second aperture shielding stray light that enters the first aperture from an adjacent reflection mirror (35a, 35b, 35c), the first aperture and the second aperture being provided in an optical path of the image light (d) between a reflection mirror (35a, 35b, 35c) and an imaging region (41a, 41b) of the sensor; and a first aperture which adjusts an amount of the image light (d) reflected from the reflection mirror (35a, 35b, 35c); and a second aperture formed between a mirror array and the first aperture, the second aperture shielding stray light that enters the first aperture from an adjacent reflection mirror (35a, 35b, 35c), the first aperture and the second aperture being provided in an optical path of the image light (d) between a reflection mirror (35a, 35b, 35c) and an imaging region (41a, 41b) of the sensor; and between the first aperture and the second aperture, a reflection reduction mechanism (S, 70, 71, 37d) is provided that reduces reflection, toward the first aperture, of light other than the image light (d) traveling from the second aperture to the first aperture, wherein the first aperture and the second aperture are openings provided in an aperture stop main body on a sensor side and on the mirror array side thereof respectively.