PURPOSE: To prevent the loss of paper and loss of time required for reprinting by deciding paper clogging through detecting the movement of sprocket holes of a continuous form and by performing the stop of printing and notification to man according to the decision signal of said paper clogging.

CONSTITUTION: A light source 1 and a photo-detector 2 provided at a printer are fixed in the position corresponding to sprocket holes B, and said photo-detector 2 detects an intermittent pulse with a given period according to a space between said sprocket holes B when a continuous form A moves by the driving signal D of a driving part 3. Since said intermittent pulse is outputted simultaneously with said driving signal D when there is no paper clogging, a comparator 4 compares the driving signal and the output of said photo-detector 2 and outputs a decision signal C of 'normal' or 'paper clogging'. That is, while the output of the photo-detector 2 is synchronized with the driving signal D and intermitted with a given period, said decision signal C is 'normal', but when the photo-detector 2 is not intermitted for more than said given period, a paper feed is decided to be abnormal and the decision signal C is 'paper clogging'.