PURPOSE: To surely detect the jamming of paper, by providing a roller which is rotated synchronously with the conveyance of continuous paper, installing a detector for the rotative state of the roller, and monitoring the output of the detector when a conveyance instruction is applied.
CONSTITUTION: A driven roller 7b is rotated synchronously with the conveyance of recording paper 1a. As a result, a slitted disc 7b3 is rotated and a photocoupler 7b5 generates a detection pulse P which shows the state of conveyance of the recording paper. When the detection pulse P is applied to a one-shot circuit 11, an "H"-level signal V is continuously produced throughout the state of conveyance. A judgement circuit 12 detects a conveyance instruction signal S and the output V to generate a signal W to raise an alarm and turn off a power source or the like. Thus, a trouble due to the jamming of the paper can be prevented.