Image reader and image forming apparatus

An image reader including a read guide disposed on both sides of a document conveyance path, the read guide having a space therein that is adjustable in accordance with a thickness of a document conveyed, comprising:

• a read frame member fixed to a document reading unit, the read frame member supporting an optical system;
• a read guide member making up a housing member together with the read frame member to accommodate the optical system therein, the read guide member being configured to guide a document to be conveyed to a reading position and support a read glass, and the read guide member being supported slidably with respect to the read frame member;
• and
• a seal mechanism covering a gap between the read frame member and the read guide member, wherein
• the seal mechanism includes a rib standing in parallel with a sliding direction of the read guide member and a flexible dustproof sheet having an end that is in contact with the rib.