PURPOSE: To enable the detection of the presence or absence of a continuous form paper and a cut paper, by providing a guide for the cut paper and two turnable pieces engaged with each other and connected to a sensor for detecting the presence or absence of a printing paper, outputting a signal through turning one of the turnable pieces when the continuous form paper or the cut paper is inserted, and returning the turntable piece after the passage of the trailing end of the paper.

CONSTITUTION: With a continuous form paper 23 inserted, one end 25 of a first turnable piece 15 is turned by the leading end of the paper 23, whereby the other end of the turnable piece is separated from a sensor 18 to open an optical path for the sensor 18, and a signal indicative of the presence of the printing paper is outputted. When printing is finished and the paper is discharged, the turnable piece 15 is returned into an original condition, and a signal corresponding to the absence of the printing paper is outputted. With a cut paper 24 inserted into the printer, on the other hand, a second turnable piece 16 is turned, the paper 24 is inserted along a paper guide plate 8 toward a platen 7, and when the trailing end (rear end) of the paper is fed past the second turnable piece 16 after predetermined printing is finished, the first turnable piece 15 is turned by a restoring force due to its own weight, thereby interrupting the optical path for the sensor 18, so that a signal corresponding to the absence of the printing paper is outputted.