| 摘要 |
PROBLEM TO BE SOLVED: To catch a subscriber line in a vacant state without operating the key again when a subscriber line catch key of the subscriber line in an in-use state is accidentally depressed as well.SOLUTION: In a principal device 10, a subscriber line use situation table 14A which stores an in-use state and a vacant state as a use situation of a subscriber line 10L in response to the catch and release of the subscriber line 10L is provided for each subscriber line 10L. A call controller 15 checks the use situation of the subscriber line 10L corresponding to a subscriber line catch key 23 with reference to the subscriber line use situation table 14A in response to depression of the subscriber line catch key 23 in a button telephone 20, catches the subscriber line 10L concerned when the use situation concerned indicates the vacant state, and selects and catches the other subscriber line 10L in the vacant state with reference to the subscriber line use situation table 14A when the use situation concerned indicates the in-use state. |
