PURPOSE: To detect the jam of documents and recording paper unlimited in length.

CONSTITUTION: Angular moment is let act upon a gear 7 by frictional force between a document or recording paper and a rubber roller 6, and a frame 8 is rotated in the direction of an arrow mark utilizing frictional force between the gear 7 and a gear 9. When the conveyance of the document or recording paper is stopped by the generation of a jam, the angular moment stops acting upon the gear 7, so that the frame 8 is returned into the original position by a coil spring 4 to shut off the light of a photo sensor. Accordingly, when the jam is generated, the action of angular moment from the gear 7 ceases to exist, so that the frame 8 is displaced being pulled by the spring. The photo sensor detects the displacement of the frame to enable the detection of the jam.