According to one embodiment, a main apparatus includes a transmitter which transmits a control signal necessary for notifying the communication connection to a first telephone terminal belonging to the group and a second telephone terminal belonging to the group, when the first telephone terminal establishes communication connection by using the line, a monitoring module configured to monitor congestion of at least an own apparatus, and a controller which controls execution and stoppage of transmission processing of the control signal to the second telephone terminal carried out by the transmitter based on a result of congestion monitoring carried out by the monitoring module.