There is provided a detection device including: a detection section detecting an image on a medium conveyed along the conveyance path or the medium; a reference member that is disposed at an opposite side of the conveyance path from the side thereof at which the illumination unit is disposed and that is provided to be rotatable with a rotation axis direction being a width direction of the medium; a test face comprising one of reflection faces of the reference member; a position detection pattern provided at the test face; a focal point detection pattern provided at the test face, the focal point detection pattern enabling detection by the detection section of a focal point; and a depth detection portion provided at the test face, the depth detection portion enabling detection by the detection section of an illumination depth of the light illuminated from a illumination unit.