The utility model discloses a telephone detector including a shell and a telephone detecting circuit arranged in the shell. The telephone detecting circuit includes a power transformer T connected with electric supply through a power line penetrated through the shell and used for converting the electric supply to 360V AC, a rectification filtering circuit connected with the power transformer T through a power switch K4, a telephone function detecting circuit connected with the rectification filtering circuit, a telephone connected with the telephone function detecting circuit and a detector fault self-checking circuit. The telephone detector provided by the utility model is simple in structure, reasonable in design, convenient to process and manufacture, stable in performance, high in working reliability and low in realization cost. A telephone maintaining period can be shortened and interference of people caused by repeated test run through a communication line is avoided. The telephone detector is convenient for promotion and use.