A scanner includes: a first mirror having a plurality of concavities configured to reflect light from a document; a sensor group having a sensor chip with a photoelectric conversion element line configured to detect light reflected by the concavity; and an aperture member having a plurality of apertures corresponding one-to-one to the concavities and disposed between the first mirror and the sensor group on an optical path of light reflected by the concavity; the equivalent f-number of the aperture being 6 or greater.