Abstract: PURPOSE:To reduce the number of operator's exclusive lines, by completely opening the operator's exclusive lines in storing a slave station incoming call, using them for other call processings, and using a time monitor circuit used for automatic callback as a storage time nomitor circuit after prescribed time. CONSTITUTION:In a telephone concentrating response system in which a remote master station operator responds to an incoming call CAST to a slave station and the incoming call is transferred to a slave station extension EXTA through the operation of the operator, when an incoming call is stored, the operator exclusive line is completely opened and usable for other call processings, and after the storing time elapses a prescribed time, the master station operator is called out. In this system, the circuit can also be used as the storage time monitoring circuit by adding a contact to the time monitor circuit used for the automatic callback.