An image reading device has a light emitting unit. The light emitting unit has a light emitting portion, a light guiding member, a holding member and a case member. The light guiding member is disposed along a main scanning direction, and an end portion of the light guiding member faces the light emitting portion. The light guiding member has a light irradiating portion which emits light to an outside. The holding member holds the light emitting portion and the light guiding member. In addition, the holding member has a first holding portion that directly or indirectly positions and holds the light emitting portion, and a second holding portion that positions and holds one end or both ends of the light guiding member. The case member houses the holding member that is in a state of being positioned.