PURPOSE: To enable independently to limit the current by each of an A line and a B line for forming telephone lines by a simple circuit constitution by providing a current limiting element which does not conduct until a feed current exceeds a prescribed value and a shows a constant-voltage when it exceeds the prescribed value.

CONSTITUTION: The circuit is provided with current limiting elements DZ1, DZ2 which are connected in parallel to both ends of resistances, 90, 95 connected between the other end of resistances 60, 65 connected to output terminals of each operational amplifier of a first and a second mutual conductance amplifiers, and do not conduct until the feed current exceeds a constant value, and shows a constant-voltage when it exceeds the prescribed value. In such a way, the maximum current of the feeding circuit can be limited independently by each of an A line and a B line by a simple constitution without providing a circuit for measuring the current value of each of the A line and the B line for forming telephone lines.