PURPOSE: To optimize the control of a printing speed by providing a stopping means for stopping the control of the printing speed based on the exposing light quantity detected when superposed materials exist around a cylinder.

CONSTITUTION: A superposed material detecting sensor 40 detects the superposed materials W and inputs an insertion terminal signal S1 indicating that the insertion of the superposed materials W is started to the stopping means 50 when the superposed materials W are inserted from an insertion port 14 into an exposing device. The stopping means 50 inputted with the signal S1 does not execute the control of the printing speed based on the exposing light quantity detected by stopping the input of the light quantity signal to a printing speed control means 30. The printing speed control means 30 holds the light quantity signal just before the stop and controls the printing speed in accordance with this light quantity signal. Then, the control is not affected by the measurement error of the exposing light quantity occurring in the reflection of the superposed materials W. The printing speed control is optimized in this way.