An image reading apparatus, comprising: a first transparent section, which is made of a transparent material and comprises an upper surface adapted to support a first original sheet a second transparent section, which is made of a transparent material and comprises an upper surface adapted to support a second original sheet conveyed by a sheet conveyer being in contact with the upper surface of the second transparent section and to pass over the upper surface; a reader unit, which comprises a plurality of light receiving elements aligned along a main scanning direction; is movable in a sub-scanning direction being orthogonal with respect to the main scanning direction; is movable in a lower area with respect to the first transparent section in the sub-scanning direction along the first transparent section to read an image formed on the first original sheet being set on the upper surface of the first transparent section; and is maintained still in a lower area with respect to the second transparent section to read the image formed on the second original sheet being conveyed by the sheet conveyer; a white reference member, located in an image readable position for the reader unit to read an image of the white reference member, the image of the white reference member read by the reader unit being recognized as a reference white color; a light reductive member, located on an inner bottom of a casing accommodating the reader unit, the light reductive member is adapted to receiving external light that reaches the inner bottom of the casing and reducing the external light by one of reflecting, absorbing, and permitting a part of the external light to transmit therethrough, wherein the light reductive member reduces the external light, when the external light passes through the second transparent section and reaches the inner bottom of the casing whilst the reader unit is in the image readable position, characterized in that the light reductive member is absent in a position, which is further from the reader unit with respect to a directly below position from the second transparent section, whilst the reader unit is in the image readable position. a first transparent section, which is made of a transparent material and comprises an upper surface adapted to support a first original sheet a second transparent section, which is made of a transparent material and comprises an upper surface adapted to support a second original sheet conveyed by a sheet conveyer being in contact with the upper surface of the second transparent section and to pass over the upper surface; a reader unit, which comprises a plurality of light receiving elements aligned along a main scanning direction; is movable in a sub-scanning direction being orthogonal with respect to the main scanning direction; is movable in a lower area with respect to the first transparent section in the sub-scanning direction along the first transparent section to read an image formed on the first original sheet being set on the upper surface of the first transparent section; and is maintained still in a lower area with respect to the second transparent section to read the image formed on the second original sheet being conveyed by the sheet conveyer; a white reference member, located in an image readable position for the reader unit to read an image of the white reference member, the image of the white reference member read by the reader unit being recognized as a reference white color; a light reductive member, located on an inner bottom of a casing accommodating the reader unit, the light reductive member is adapted to receiving external light that reaches the inner bottom of the casing and reducing the external light by one of reflecting, absorbing, and permitting a part of the external light to transmit therethrough, wherein the light reductive member reduces the external light, when the external light passes through the second transparent section and reaches the inner bottom of the casing whilst the reader unit is in the image readable position, characterized in that the light reductive member is absent in a position, which is further from the reader unit with respect to a directly below position from the second transparent section, whilst the reader unit is in the image readable position.