PURPOSE: To enhance the services to the customers by distributing in preference the call having the highest hardness to each manual switchboard group among those calls under the hardness of each manual switchboard.

CONSTITUTION: The incoming calls are grouped into e.g. QC0, QC1 and QC2 according the handling hardness, and at the same time plural units of manual switchboards are divided into QP0, QP1 and QP2 each according to the hardness of the incoming calls. Thus in case the operator of group QP2 becomes free, the presence of the queuing calls for groups QC0∼QC2 is detected. And if the queuing call exists in group QC0, this call is connected in preference. While in case no queuing call exists, the call in group QC1 is connected. And in case no queuing call exists in group QC1, the call in group QC2 is connected for distribution. In the same way, if the operator of group QP1 is free, the call in group QC0 cannot be distributed since it is beyond the operator's capacity. Thus the calls to be connected and distributed are looked for in the order of QC1 and QC2. In such way, the calls are distributed in accordance with the capacity of the switchboard operator, thus enhancing the services to the customers.