To provide an image reading device of a sheet-through system, capable of effectively correcting a concentration of at least a tip portion of a document to obtain a high-quality read image.

An image reading device comprises: conveyance means 3 for conveying a document one by one; reading means 50 for reading an image of the document being conveyed by the conveyance means 3, at a reading position A; an upstream side guide member 33 positioned on an upstream side of the reading position A in a conveyance direction of the document, and changing the document to an approximately horizontal direction by contact of the document being conveyed; a downstream side guide member 34 positioned on a downstream side of the reading position A in the conveyance direction of the document, and changing the document downward by contact of the document being conveyed; and control means 60 for changing an illumination light amount of the reading means 50 on the basis of rigidity of the document being conveyed, or correcting a concentration of the read image.