To enable a signal to be generated by a cylinder to be simply and positively transmitted to the outside by arranging a device which is controllable in accordance with the signal from register pins and generates a magnetic field on the cylinder and also arranging a sensor which collaborates with the device for generating the magnetic field when the cylinder is set at a specified position on an evaluation unit.

On a cylinder 1, register pins 2.1, 2.2 which are electrically responsive are fitted opposite to the cylinder 1. It is interpreted with these pins 2 whether a metal printing plate can establish a correct contact through registration, in the same fashion as a switch operation. A signal generator 4 is connected on the output side so that the generator 4 can communicate with the coil of a magnet 5 with signal transmission. Thus the coil is energized when the registering position of the printing plate detected by the pins 2 is correct. In addition, a sensor 6 which detects a magnetic field is arranged in such a manner that the sensor 6 is opposite to the magnet 5 when the cylinder 1 is positioned as specified and at the same time, is connected in such a way that the sensor 6 communicates with an evaluation unit 7 with signal transmission on the output side.