To provide a sheet printing machine provided with a sensor capable of surely detecting the floating of a sheet from a carrying cylinder.

A sensor body 30 is a touch limit switch of a type so that it regularly oscillates a high-frequency wave, stops oscillation upon the contact of a conductive body with an antenna unit 31 due to change in a constant of an oscillation circuit, and a switching circuit is operated to output an output signal. Thus, an operating force of the switch is dispensed with, and minute displacement can be detected. Namely, even the slight contact of a sheet P thereto can be detected.