Abstract: A discharging element energizing circuit for a discharge-type fire alarm sensor unit including a discharging element, wherein a power supply circuit gives a power voltage to the discharging element in the form of periodical output pulses making same ready to discharge and a feedback circuit is provided to supply a feedback signal obtained from the discharging element to the power supply circuit so as to vary the interval of the output pulses. The sensor unit is continuously sensitive to ultraviolet rays only caused by a fire disaster, thus preventing a malfunctional alarm. Power consumption is reduced considerably, allowing the unit to be operated with commercially available dry cells.