A system according to this invention is directed to a virtual network system that prevents unauthorized registration, alteration, or occurrence of erroneous registration even if an operator is to create a network system including a virtual network function produced by a third party. The virtual network system includes an instructor that instructs activation or change of a virtual network function preregistered of providing one of functions included in a virtual network service, an authenticator that authenticates, based on authentication information generated to authenticate a provider of the virtual network function at a time of registering the virtual network function, that the virtual network function instructed to be activated or changed has been validly registered or updated, and a setting unit that sets, when the authenticator authenticates that the virtual network function has been validly registered or updated, the instructed virtual network function as the one of the functions included in the virtual network service.