A virtual network system (100, 200) comprising: an authentication server configured to store a plurality of pieces of authentication information (702-722, 733-743, 772), each associated with a VNF, virtual network function identifier, and with a VNF provider identifier (701-721, 732-742, 771) which represents a provider of a VNF, and wherein the authentication information is generated to include both VNF function information and VNF provider information; a registration apparatus configured to register a plurality of virtual network functions (706-726, 737-747, 776), each associated with a VNF function identifier and with a VNF provider identifier (705-725, 736-746, 775), respectively; and a control apparatus configured to: receive, from an operator terminal, an instruction which represents activation or change of a virtual network function, and a VNF function identifier and a VNF provider identifier of the instructed virtual network function; authenticate that the instructed virtual network function is valid, according to the received VNF function identifier and VNF provider identifier, using the plurality of pieces of authentication information (702-722, 733-743, 772) stored in the authentication server; and perform the activation or the change of the instructed virtual network function in response to a status that the instructed virtual network function corresponds to the received VNF function identifier and VNF provider identifier, using the plurality of virtual network functions (706-726, 737-747, 776) associated with the plurality of VNF function identifiers and VNF provider identifiers (705-725, 736-746, 775) registered in the registration apparatus; wherein the authentication server is configured to store as the authentication information a verification key (712, 722, 733, 743) in association with the VNF identifier and the VNF provider identifier, wherein the verification key (712, 722, 733 and 743) is generated to include VNF function information, VNF provider information and operator information, wherein the operator is the operator who has input the instruction which represents the activation or change of a virtual network function. an authentication server configured to store a plurality of pieces of authentication information (702-722, 733-743, 772), each associated with a VNF, virtual network function identifier, and with a VNF provider identifier (701-721, 732-742, 771) which represents a provider of a VNF, and wherein the authentication information is generated to include both VNF function information and VNF provider information; a registration apparatus configured to register a plurality of virtual network functions (706-726, 737-747, 776), each associated with a VNF function identifier and with a VNF provider identifier (705-725, 736-746, 775), respectively; and a control apparatus configured to: receive, from an operator terminal, an instruction which represents activation or change of a virtual network function, and a VNF function identifier and a VNF provider identifier of the instructed virtual network function; authenticate that the instructed virtual network function is valid, according to the received VNF function identifier and VNF provider identifier, using the plurality of pieces of authentication information (702-722, 733-743, 772) stored in the authentication server; and perform the activation or the change of the instructed virtual network function in response to a status that the instructed virtual network function corresponds to the received VNF function identifier and VNF provider identifier, using the plurality of virtual network functions (706-726, 737-747, 776) associated with the plurality of VNF function identifiers and VNF provider identifiers (705-725, 736-746, 775) registered in the registration apparatus; receive, from an operator terminal, an instruction which represents activation or change of a virtual network function, and a VNF function identifier and a VNF provider identifier of the instructed virtual network function; authenticate that the instructed virtual network function is valid, according to the received VNF function identifier and VNF provider identifier, using the plurality of pieces of authentication information (702-722, 733-743, 772) stored in the authentication server; and perform the activation or the change of the instructed virtual network function in response to a status that the instructed virtual network function corresponds to the received VNF function identifier and VNF provider identifier, using the plurality of virtual network functions (706-726, 737-747, 776) associated with the plurality of VNF function identifiers and VNF provider identifiers (705-725, 736-746, 775) registered in the registration apparatus; wherein the authentication server is configured to store as the authentication information a verification key (712, 722, 733, 743) in association with the VNF identifier and the VNF provider identifier, wherein the verification key (712, 722, 733 and 743) is generated to include VNF function information, VNF provider information and operator information, wherein the operator is the operator who has input the instruction which represents the activation or change of a virtual network function.