A controller 70 of an image reading device 1 acquires first black reference data at a first time point with a light source 31 off, and stores the first black reference data in a reference data storage 41, and at a second time point after the first time point, acquires with the light source 31 off and stores second black reference data in the reference data storage 41. The controller 70 stores in a scanning data storage 42, without applying shading correction, scanning data read from a document between the first time point and second time point with the light source 31 on. A shading corrector 51 applies shading correction using the first black reference data and second black reference data to the scanning data stored in the scanning data storage 42.