a circuit for controllably driving a heater in order to speed up temperature elevation at a buildup stage of a liquid which is to be maintained at a predetermined temperature heated by the heater , particularly ink in an ink jet printer . a voltage developed by doubling an output voltage of an atmospheric temperature sensor by an amplifier is compared with a reference voltage , which is adapted to decide power to be supplied to the heater in the event of a buildup of the ink temperature . a temperature - sensitive element responsive to an atmospheric temperature has a temperature coefficient which is double the temperature coefficient of a temperature - sensitive element responsive to a heater temperature . the output voltages of the two elements are weighted by a same amount and then added together , the summation output being compared with the reference voltage .