To provide a security system capable of utilizing a phone to cope with a visitor without the need for large scale wiring works and facilitates.

The entry restriction facility controller D controls auto locking of a community entrance E and connects with a pink public phone C installed in an entrance hall B. The entry restriction facility controller D stores a telephone number of phone in each room of a mansion A, and interrupts only a line connected to the pink public phone C when detecting a prescribed signal during a speech with the telephone number stored in the pink public phone C. When the entry restriction facility controller D detects a prescribed signal succeedingly after the interruption of line with the pink public phone C, the entry restriction facility controller D unlocks the auto lock of the community entrance E.