The image reading device includes a light emitting portion, stick-like light guiding member, holding member and case member. An end portion the light guiding member is disposed to face the light emitting portion. The holding member holds the light emitting portion and the light guiding member. The holding member has first and second positioned portions. The first and second positioned portions are formed at one end part and another end part of the holding member in a main scanning direction, respectively. The holding member is attached to the case member. The case member has first and second positioning portions. The first and second positioning portions are formed integrally with the case member. The first and second positioning portions are configured to restrict the inserted first and second positioned portions from moving in a direction transverse to the main scanning direction, respectively.