PURPOSE: To reduce a practical capacity of each heater and to reduce the maximum electric capacity of whole apparatus of an automatic developing machine by applying pulse voltage to each heater alternately when it is necessary to supply power to plural heaters.

CONSTITUTION: When the temperature of a treating solution rises and reaches to a set temperature, the output of a comparator 11 is turned to L and power supply to a treating solution heater stops. If a photosensitive material is inserted into a processing equipment under said condition, the output of a cycle counter is turned to H, so that the output of an AND circuit 25 is turned to H and the output of a timer 24 is kept at ON for a fixed period T. After the period T has passed, the output of the timer 24 is turned to L, and when the output of only one comparator out of the comparators 11, 12 is H, current is continuously supplied to only one heater out of the treating solution heater 4 and a drying heater 5. When the outputs of both comparators 11, 12 are H, current is supplied to the treating solution heater 4 if the output OS1 of an oscillator 20 is H, and current is supplied to the drying heater 5 if the output OS2 of the oscillator 20 is H. Since the temperature of the treating solution and a drying part is almost kept at the set temperature, the set temperature can be maintained sufficiently only by applying the pulse voltage.