PURPOSE: To insure a line against being cut by preventing the off state of a hook switch from being out putted even if a handset is placed in the middle of automatically transmitting a holding request signal to an exchange from a telephone set.

CONSTITUTION: An AND circuit 13 functions as a gate to inhibit or permit the state output of the hook switch 11. A holding button 14 is depressed when a holding request is issued. A holding request detection circuit 15 detects the depression of the holding button 14, and activates a timer circuit 16. It is set to operate in a period set by a timer longer than the length of the holding request signal. Its output in stoppage is of a voltage at one level, and becomes a voltage at '0' level when the timer circuit 16 is activated by the holding request detection circuit 15. When the circuit 16 reaches the time that the timer sets, it agains outputs '1' level voltage, which is impressed on the other input of the AND circuit 13. Thus even if the handset is placed right after the holding button is depressed, nothing to cut the line.