Image reading apparatus provided with a white reference member for shading correction

An image reading apparatus comprising:

• an image reading portion which is unmovably arranged at one side with respect to a document transportation path;
• a white reference member for shading correction which is arranged at the other side with respect to the document transportation path, the white reference member having a white reference surface for shading correction and a sheet feeding surface;
• a cover member which is capable of being opened and closed so as to expose or cover the document transportation path, wherein the white reference member is attached to the cover member;
• and
• a driving unit which changes a posture of the white reference member between an operating posture at the time of the shading correction in which the white reference surface is opposed to the image reading portion and a non-operating posture at the time of a document transportation in which the sheet feeding surface is opposed to the image reading portion, wherein the driving unit has a transmission cutting member that is a gear member of which engagement is released with an opening operation of the cover member, and blocks transmission of a driving force to the white reference member when the cover member is opened and the white reference member is placed into a free state where a posture of the white reference member is not changed by the driving unit with an operation of the transmission cutting member, and
• the white reference member and the driving unit are related to each other such that when the white reference member is in the non-operating posture before the opening operation of the cover member, the white reference member remains in the non-operating posture irrespective of the opening operation of the cover member.