An image reader includes a path switching part, located at a branch point that switches between a double-sided path and a single-sided path. The double-sided path defines a conveyance route that passes through a reading position from the branch point to enter a conveyance path that causes a document to make a U-turn, and then again passes through the reading position to be discharged to a paper discharge tray. The single-sided path defines a conveyance route that, without passing through the reading position, merges into the conveyance path from the branch point. Along the double-sided path, document detecting sensors provide detection results so that a collision determination part determines a possibility of a collision between documents, and if such a possibility is determined, the path switching part switches the double-sided path to the single-sided path to prevent the documents from colliding head-on with each other in the vicinity of the reading position.