PURPOSE: To prevent the reduction of the service life of neon tubes by adjusting a supply current to the neon tubes when the number of the neon tubes of plural subscriber terminal equipments in parallel reaches a few when a booster battery power is supplied to the plural subscriber terminal equipments in parallel via a current control circuit.

CONSTITUTION: In a circuit providing the output of a power of a booster battery VB supplied to subscriber terminal equipment, a voltage monitor section 17 monitors an output voltage VT and controls drive/release of a BS relay 18 when the voltage reaches a predetermined voltage and a current control section 19 inserting/short-circuiting a Zener diode Z with a contact bs of the BS relay 18 is provided. Thus, in the case of a few eon tube circuits, e.g. one neon tube circuit (subscriber terminal equipment), the voltage monitor section controls and limits the current supplied to the subscriber terminal equipment at the voltage in this state, the service life of the neon tube is prolonged.