An image reading device includes contact glass, a frame, a light emitting section, a sensor, and a control section. An original document is placed on the contact glass. The flame surrounds the periphery of the contact glass. The light emitting section emits light toward the contact glass and the frame. The sensor detects a first received light amount resulting from first reflected light that has passed through the contact glass and a second received light amount resulting from second reflected light that has been reflected off the frame. The control section compares temporal variation of the first received light amount with temporal variation of the second received light amount. The control section determines whether or not the temporal variation of the first received light amount indicates presence of the original document on the contact glass using the temporal variation of the second received light amount as a reference.