An object is to provide a communication system capable of preventing a number of control signals, which could occur in a mobile communication network, from occurring when a VM is deleted in a node device without suspending a service. A communication system according to the present invention includes a communication device 1, and a communication device 2 configured to control a plurality of sessions set between the communication devices 1 and 2 by using a plurality of VMs, in which the communication device 2 notifies, by using a determination that a plurality of sessions that are controlled between the communication device 1 and a VM 3 should be controlled in a VM 4 different from the VM 3 as a trigger, the communication device 1 of identification information used in the VM 4 and updates the sessions.