PURPOSE: To offer an exchange provided with an incoming call priority condition collating function for a telephone set in conversation to make it possible to deal with only an incoming call conforming to a priority condition the user of the telephone set determines beforehand by the telephone set when the incoming call terminates at the telephone set in conversation.

CONSTITUTION: The title exchange is constituted as follows. In the case that the incoming call terminates at the telephone set in a communicating state controlled by the exchange from a line wire and priority information is included in an incoming call signal, the priority information is collated with the information of the storage part 101-3 of the exchange to store the prescribed priority information of a terminating telephone set, and only when the priority information included in the above-mentioned incoming call signal satisfies a condition the above-mentioned callee determines, a call waiting signal is sent to the above- mentioned terminating telephone set.