A position detection device, comprising: a background member having a higher absorption characteristic in an invisible wavelength region than in a visible wavelength region; a reader disposed opposite the background member and configured to irradiate a recording medium having a mark and the background member with light of a visible wavelength to output a visible image or with light of an invisible wavelength to output an invisible image; a position detection unit configured to detect an end position of the recording medium and a position of the mark on the recording medium from a read image output from the reader; and a control unit configured to select the visible image or the invisible image as the read image which the position detection unit uses for position detection, according to an absorption characteristic of a color material forming the mark read by the reader and an absorption characteristic of the recording medium in the invisible wavelength region, characterized in that the control unit is configured to cause the position detection unit to perform the position detection using the invisible image as the read image when the reader reads a recording medium on which the mark is formed with a color material having a higher absorption characteristic than the recording medium in the invisible wavelength region and having a lower absorption characteristic than the background member in the invisible wavelength region and in that the control unit is configured to cause the position detection unit to perform the position detection using the visible image as the read image when the reader reads the recording medium on which the mark is not formed with a color material having a higher absorption characteristic than the recording medium in the invisible wavelength region or when the reader reads a recording medium having no lower absorption characteristic than the background member in the invisible wavelength region. a background member having a higher absorption characteristic in an invisible wavelength region than in a visible wavelength region; a reader disposed opposite the background member and configured to irradiate a recording medium having a mark and the background member with light of a visible wavelength to output a visible image or with light of an invisible wavelength to output an invisible image; a position detection unit configured to detect an end position of the recording medium and a position of the mark on the recording medium from a read image output from the reader; and a control unit configured to select the visible image or the invisible image as the read image which the position detection unit uses for position detection, according to an absorption characteristic of a color material forming the mark read by the reader and an absorption characteristic of the recording medium in the invisible wavelength region, characterized in that the control unit is configured to cause the position detection unit to perform the position detection using the invisible image as the read image when the reader reads a recording medium on which the mark is formed with a color material having a higher absorption characteristic than the recording medium in the invisible wavelength region and having a lower absorption characteristic than the background member in the invisible wavelength region and in that the control unit is configured to cause the position detection unit to perform the position detection using the visible image as the read image when the reader reads the recording medium on which the mark is not formed with a color material having a higher absorption characteristic than the recording medium in the invisible wavelength region or when the reader reads a recording medium having no lower absorption characteristic than the background member in the invisible wavelength region.