PURPOSE: To improve the reliability by providing a rectifier circuit having a voltage adjustment element to an input section of a terminal feeding power supply of a digital line terminator (DSU).

CONSTITUTION: A terminal feeding power supply 11 is energized via diodes D1, D2 in a rectifier circuit 12 because a DSU input L2 is positive at talking and the power supply 11 is energized via DSU inputs D3, D4 in the rectifier circuit 12 because the DSU input L1 is positive at standby. Then a terminal equipment 3 is energized by the power supply 11 in one circuit both in talking and standby states and the hardware is saved. Moreover, an input voltage in the standby state is increased more than that in the talking state, but the input to the power supply 11 is made constant by a voltage regulating element 13.