A telephone hook switch in a telephone includes: a capacitive sensor having a capacitance that varies when an object or a part of a human body having a charge contacts or approaches it; and a signal generation circuit for detecting the variation of the capacitance of the capacitive sensor when the object or the part of the human body contacts or approaches so as to generate an ON/OFF signal. As a result of the invention, mechanical and structural limitations on the telephone are overcome, and the economic use of an inner space of the telephone can be improved. In addition, various applications can be made to conform to an external shape of the telephone in terms of design.