To spread sheet paper to be flattened while minimizing generation of noise.

On a part of a paper discharging device continuous with a processing station at the rearmost part of a printing machine, a flattening device is provided. This flattening device 5 comprises a flattening groove 5.3 provided in a surface to guide the sheet paper, and a suction chamber 5.2 of a sound eliminating structure communicated with it. An inner space 5.7 of the suction chamber 5.2 is connected to a negative pressure generating device 5.1 and the flattening groove 5.3 respectively through a suction connection tube 5.5 and a suction opening 5.6. As the suction chamber 5.3 is set at negative pressure by actuation of the negative pressure generating device 5.1, the sheet paper is sucked to the flattening groove 5.3 to be flattened. After the sheet paper passes the flattening groove 5.3, the negative pressure in the suction chamber 5.2 is quickly released, when noise is generated, but the noise is restricted because of the sound eliminating structure of the suction chamber 5.2 where the noise is generated.