PURPOSE: To perform a rapid reaching of an injection nozzle to its target position, restrict a heat generation at a motor and improve durability of a hot water feeder by a method wherein a feed-forward control and a feed-back control are combined to each other.

CONSTITUTION: At a control part 30, the number of output value of a required rate of combustion calorie of a burner is calculated in reference to a set hot water feeding-out temperature and a feeding water flow rate. A feed-forward control is carried out up to an advancing position (the number of steps of a stepping motor 12) of the nozzle 11 corresponding to the calculated number of outputs in reference to a relation between the number of outputs and the injection nozzle position. This control is carried out by outputting the stepping motor 12 up to the calculated number of steps. Then, the actual fed-out hot water temperature and a set outputted hot water temperature are compared to each other at the control part 30 and then a feed-back control is carried out at a control value corresponding to the difference. This control is carried out by intermittently outputting the driving pulse of the stepping motor with a width variation outputting system.