PURPOSE: To provide the exchange processing a call from an external line terminal equipment whose call received again with priority.

CONSTITUTION: When a call comes from any of external terminal equipments 4a-4d, a trunk line interface 14 detects a dial telephone number and a call reception time from the external terminal equipments 4a-4d. A central controller 11 stores the detected dial telephone number and call reception time to a number table 121 of a main storage device 12 as to each of the external terminal equipments 4a-4d whose call arrives. When any of extension terminal equipments 3a-3c changes from a reply state into a talking available state, the central controller 11 detects the dial telephone number corresponding to the earliest call reception time from the number table 121 and connects the external terminal equipments 4a-4d of the detected dial telephone number among the external terminal equipments 4a-4d in the call waiting state to the extension terminal equipments 3a-3c in the talking available state with priority and deletes the dial telephone number and the call reception time of the external terminal equipments 4a-4d connected with priority from the number table 121.