PURPOSE: To enable accurate detection of the lateral size and the displacement of a paper by arranging two split rollers having the outer circumferential face made of conductive material on a same axis while isolating each other and crossing perpendicularly to a paper feed path then connecting a resistor and a power supply in series therewith.

CONSTITUTION: Split rollers 12, 13 are arranged on a same axis while being separated by a distance (s) from the center 25 of the roller, and thereby they are isolated each other. Resistors 26, 27 and power supplies, i.e., batteries 28, 29, are connected with right and left bearings respectively, where voltage detecting sections 30, 31 are connected across the resistors 26, 27 and the frame 17 is grounded. Outer circumference of the split rollers 12, 13, made of conductive rubber, is deformed elastically by the resistance of a paper 2 and a portion where there is no paper contacts with a roller 11. Since the voltages V1, V2 detected through the voltage detecting sections 30, 31 vary continuously corresponding to the lateral position of the paper 2, lateral size and displacement of the paper 2 can be detected accurately.