Image reading apparatus and image forming apparatus having inclined planar shape of background member to improve sheet shadow detection accuracy

An image forming apparatus comprising:

• a conveyance member configured to convey a sheet;
• a transparent member;
• a background member disposed opposite the transparent member;
• a reading unit disposed on a side of the transparent member opposite the background member, the reading unit including a light source and a reading sensor;
• and
• an image forming unit configured to form an image on a sheet based on image information read by the reading unit,
• wherein the light source includes a first illumination portion and a second illumination portion, and is configured to emit light toward a sheet, and the reading sensor is configured to read, through the transparent member, a shadow of the sheet projected onto the background member and an image of the sheet,
• wherein, as viewed in a width direction perpendicular to a conveyance direction of a sheet, an irradiating direction of first light emitted from the first illumination portion is inclined toward a downstream side in the conveyance direction, an irradiating direction of second light emitted from the second illumination portion is inclined toward an upstream side in the conveyance direction,
• wherein the background member has a planar shape inclined such that, in the conveyance direction, a downstream side of the background member is closer to the transparent member than an upstream side of the background member,
• wherein, as viewed in the width direction, a first angle formed between the irradiating direction of the first light and a normal direction of the planar shape is smaller than a second angle formed between the irradiating direction of the second light and the normal direction, and
• wherein the reading sensor is configured to read the first light and the second light reflected from the background member and passing through a predetermined region of the transparent member, the predetermined region being positioned between the first illumination portion and the second illumination portion in the conveyance direction when viewed in the width direction.