An image reading device wherein transfer pathways intersect at the time of double-side reading, and by which frontal collision of original documents and extensive damage applied to the original documents can be prevented. A path switch unit (17) which switches between a double-side path and a single-side path is provided at a branch point (C1). The double-side path comprises a transfer pathway which starts from the branch point (C1), passes a reading position (C2), enters transfer path (B3) where the original document (A) turns around, and thereafter, passes the reading position (C2) again, and reaches a paper receiving tray (12) to which the original document is discharged. On the other hand, a single-side path comprises a transfer pathway which starts from the branch point (C1) and merges to the transfer path (B3) without passing the reading position (C2). On the double-side path, original document detection sensors (DS4 and DS5) are provided, and on the basis of the detection results from the sensors, a collision assessment unit (32) assesses the possibility of a collision between the original documents. If it is determined that the collision is to occur, the path switch unit (17) switches from the double-side path to the single-side path, to thereby prevent the frontal collision of original documents near the reading position (C2).