A network device to be connected with a communication network, the network device capable of executing a communication function by utilizing the communication network, the network device comprising: an input device configured to input communication setting data for executing the communication function; a storage capable of storing a pattern of the communication setting data; a communication device configured to execute the communication function by utilizing one pattern of the communication setting data stored in the storage; and a communication test device configured to test whether it is possible to execute the communication function by utilizing an other pattern of the communication setting data while maintaining a state where it is possible for the communication device to execute the communication function by utilizing the one pattern of the communication setting data, wherein the network device is configured to be connected with at least one terminal device in a communicable manner via the communication network; the input device is configured to input communication setting data output by the terminal device via the communication network in a case where the communication device executes the communication function by utilizing the one pattern of the communication setting data; the communication network is an internet; said other pattern of the communication setting data is stored in the storage while maintaining a state where it is possible for the communication device to execute the communication function by utilizing the one pattern; the network device further comprises an electronic mail analyzing device; wherein the communication setting data includes setting data for sending and/or receiving an electronic mail; the input device is configured to input an electronic mail output by the terminal device in a case where the communication device executes the communication function by utilizing the one pattern of the communication setting data; the electronic mail analyzing device is configured to determine communication setting data included in the electronic mail input to the input device, and the storage is configured to store the communication setting data determined by the electronic mail analyzing device as said other pattern. an input device configured to input communication setting data for executing the communication function; a storage capable of storing a pattern of the communication setting data; a communication device configured to execute the communication function by utilizing one pattern of the communication setting data stored in the storage; and a communication test device configured to test whether it is possible to execute the communication function by utilizing an other pattern of the communication setting data while maintaining a state where it is possible for the communication device to execute the communication function by utilizing the one pattern of the communication setting data, wherein the network device is configured to be connected with at least one terminal device in a communicable manner via the communication network; the input device is configured to input communication setting data output by the terminal device via the communication network in a case where the communication device executes the communication function by utilizing the one pattern of the communication setting data; the communication network is an internet; said other pattern of the communication setting data is stored in the storage while maintaining a state where it is possible for the communication device to execute the communication function by utilizing the one pattern; the network device further comprises an electronic mail analyzing device; wherein the communication setting data includes setting data for sending and/or receiving an electronic mail; the input device is configured to input an electronic mail output by the terminal device in a case where the communication device executes the communication function by utilizing the one pattern of the communication setting data; the electronic mail analyzing device is configured to determine communication setting data included in the electronic mail input to the input device, and the storage is configured to store the communication setting data determined by the electronic mail analyzing device as said other pattern.