PURPOSE: To allow the operator of an attendant board accommodated in an exchange to grasp the state of a call of an attendant board incoming call waiting state, that is, the incoming call resident state with a concrete figure such as a resident call unit or a resident rate.

CONSTITUTION: An incoming call resident state monitor section 6 monitors a rate of a incoming call resident unit to an incoming call resident number or a maximum allowable wait call unit of an incoming call queue 5 for each attendant board group accommodated in an exchange 4. An incoming call resident state signal transmission section 7 sends a signal representing the resident call unit or the resident rate monitored by the incoming call resident state monitor section 6 to an attendant board 1. An incoming call resident state display control section 2 receives an incoming call resident state signal 8 to display the incoming call resident state onto an incoming call resident state display window 3.