TELEPHONE LINE/DOORPHONE SWITCHING ADAPTOR

摘要

PROBLEM TO BE SOLVED: To provide a telephone line/doorphone switching adaptor that executes normal communication even when a telephone line is changed into a digital channel. SOLUTION: A current detection circuit 12 that is connected in series with a telephone line L to detect an operating state of the telephone line L is configured such that increase in the resistance of the circuit 12 can be suppressed against passing of a high frequency signal through the circuit 12.