In a lighting device, a light source emits light. A second sandwiching member includes a second opposed surface opposing a first opposed surface of a first sandwiching member. The first sandwiching member and the second sandwiching member sandwich the light source in such a manner that the light source is detachably attached to the first sandwiching member and the second sandwiching member. A reflection member is provided on the first opposed surface of the first sandwiching member and the second opposed surface of the second sandwiching member to reflect the light emitted by the light source toward an irradiation region on an original document sheet. A positioning member is provided in the first opposed surface of the first sandwiching member and the second opposed surface of the second sandwiching member to position the light source with respect to the reflection member.