A sheet presser including two pivot shaft portions fixedly disposed substantially coaxially with each other and parallel to a sheet of a document conveyed in a direction; a pressing member mounted on the shaft portions; a biasing member biasing the pressing member around the shaft portions in a direction to press the sheet; the pressing member having two elongate bearing bores each long in a direction substantially perpendicular to a surface of the sheet, which are formed in respective portions which are distant in a lateral direction of the pressing member to bear the shaft portions; and the biasing member biasing the pressing member such that at least one of the shaft portions is held in contact with one end of the bearing bore which is away from the sheet, so that an acute angle formed between the conveyance direction and the pressing member is within a predetermined range.