PURPOSE: To obtain invariably a stable copy by taking the humidified cloth out of a water tank by a drawing-out device at need, and humidifying paper in a roll paper supply device.

CONSTITUTION: When a main switch 26 is turned on, a rising signal generating circuit 24 outputs pulses for a specified time. On the other hand, if a form is dry, a comparator 23 outputs "1" and an AND gate 25 also outputs "1" to turn a rotary solenoid 14; the humidified cloth 7 is taken out of the water in the water tank 5 and made wet appropriately by a squeeze roll 12 to cover roll paper 29. This humidified cloth 7 is held in an invariably constant wet state. When the humidity of the roll paper 29 exceeds a specified value, the comparator 23 outputs "0" and a latch solenoid 21 is reset by its inverted signal, i.e. a rising pulse signal. Consequently, the humidified cloth 7 is drawn in the water tank 5 by an energizing spring 9.