PURPOSE: To finish uniformly photosensitive paper density corresponding to the transmittivity of an original by counting the number of pulses synchronizing with the speed of a copying machine driving motor and deciding on the time when automatic printing control is reset.

CONSTITUTION: When the original is at the entrance of a printing machine, a timing circuit 27 is turned on and the original transmittivity is converted by a converting circuit 28 for a driving motor speed control signal into the speed control signal of the driving motor 14, which puts a driving motor speed control circuit 29 in operation to control the speed of the motor 14. The number of pulses generated synchronously with the speed of the motor 14 according to the distance from an original insertion sensor to a printing part passing point is counted by a counting circuit 30 previously set to specific timing. Therefore, the circuit 30 resets the circuit 29 according to the specified number of pulses from the pulse generator after the point of time when the rear end of the original passes by the original insertion detecting sensor and turns off this sensor, returning the motor 14 to a constant-speed state.