PURPOSE: To detect a sheet of recording paper to be conveyed in succession so accurately, by installing a step difference in a guide plate, and setting up a photosensor so as to cause an optical axis to go across this step difference.

CONSTITUTION: A conveying guide plate 6 is divided upper guide parts 6a and 6b and lower guide parts 6c and 6d, respectively, and both these guide parts 6a and 6c are bent downward at the specified angle, forming each of inclined step parts A and B. A transmission type photosensor 5 is set up so as to cause an optical axis to go across these inclined step parts A and B. In consequence, there is possible to take sufficient distance between a rear end of recording paper 7 to be conveyed along the guide plate 6a and a tip of another recording paper 8 and thereby to take sufficient time long for detecting a clearance between these recording paper sheets by the photosensor 5, so that each sheet of the recording paper to be conveyed in succession is accurately detectable.