A light detection device comprising: a first detecting portion to detect fluorescence from a first detection position on a conveyor path along which a sheet is conveyed; characterized in that a second detecting portion to detect afterglow from a second detection position on the conveyor path along which the sheet is conveyed; a lighting portion to apply excitation light over a range including the first detection position and not including the second detection position; a shield plate to block the light emitted from the lighting portion to enter the second detection portion; a first reference member to emit reference light toward the first detecting portion, the first reference member including fluorescent material which emits fluorescence by being excited by the lighting portion; a second reference member to emit reference light toward the second detecting portion when the sheet is absent at the second detection position and to emit reference light toward the second detecting portion when the sheet is present at the second detection position, the reference light not influencing a result of detection by the second detecting portion, the second reference member being disposed to be separated from the second detection position by a predetermined distance along an optical path, and emits diffuse reference light, and the second reference member including fluorescent material which emits fluorescence by being excited by the lighting portion, and being disposed at a position which the light emitted from the lighting portion enters; and a correction controller to correct a result of detection by the first detecting portion based on the reference light detected by the first detecting portion and to correct a result of detection by the second detecting portion based on the reference light detected by the second detecting portion. a first detecting portion to detect fluorescence from a first detection position on a conveyor path along which a sheet is conveyed; characterized in that a second detecting portion to detect afterglow from a second detection position on the conveyor path along which the sheet is conveyed; a lighting portion to apply excitation light over a range including the first detection position and not including the second detection position; a shield plate to block the light emitted from the lighting portion to enter the second detection portion; a first reference member to emit reference light toward the first detecting portion, the first reference member including fluorescent material which emits fluorescence by being excited by the lighting portion; a second reference member to emit reference light toward the second detecting portion when the sheet is absent at the second detection position and to emit reference light toward the second detecting portion when the sheet is present at the second detection position, the reference light not influencing a result of detection by the second detecting portion, the second reference member being disposed to be separated from the second detection position by a predetermined distance along an optical path, and emits diffuse reference light, and the second reference member including fluorescent material which emits fluorescence by being excited by the lighting portion, and being disposed at a position which the light emitted from the lighting portion enters; and a correction controller to correct a result of detection by the first detecting portion based on the reference light detected by the first detecting portion and to correct a result of detection by the second detecting portion based on the reference light detected by the second detecting portion.