To provide a pump controlling device, suppressing the cost of the device capable of properly setting a drive voltage, applied on a drive pump for a pump connected to hot water piping, according to piping resistance of the hot water piping.

Map data 63, 64, and 65 indicating a correlation between the drive voltage of a motor 70 needed to feed hot water to the hot water piping with a head of a given level and the number of revolutions of the motor 70 when the drive voltage is applied are pre-stored in a memory 62. A voltage control means 611 controls a drive voltage, applied on the motor 70 such that the number of revolutions of the motor 70 detected by a number of revolutions sensor 71 when the drive voltage is applied is approximately coincided with the number of revolutions obtained by applying the drive voltage to the map data.