An image scanning device includes a white reference board 104 with a uniform white color, an irradiation device 601, an image sensor 207, and a determination device 602. The irradiation device 601 includes a light source unit to irradiate a reflection side of the white reference board 104 from only one oblique direction. The image sensor 207 is configured to detect reflected light from the white reference board 104. The determination device 602 is configured to determine if an attached substance exists on the reflection side of the white reference board 104 based on the reflected light detected by the image sensor 207.