A communication device comprising: a receiving unit that is configured to receive, from a terminal device, input values for each of a plurality of setting items, the plurality of setting items including a plurality of related setting items that are related to each other and concern network settings; a first determining unit (S220, S330, S420) that is configured to determine whether the input values, received for the related setting items, that are related to each other, are compatible; and a sending unit that is configured to send, to the terminal device, error data indicating an error screen when the input values received for the related setting items are determined to be incompatible, the error screen showing that at least one input value among the plurality of input values has an error; wherein one of: the communication device further comprises a first storing unit that is configured to store reference values corresponding to the plurality of related setting items, and the first determining unit determines that the input values received for the plurality of related setting items are incompatible when the input values received for the plurality of related setting items do not match the reference values; and the communication device further comprises a verifying unit that is configured to verify that one input value among the input values received for the related setting items falls within a range that is defined by another input value among the input values for the related setting items, and the first determining unit determines that the input values received for the plurality of related setting items are incompatible when the one input value does not fall within the range. a receiving unit that is configured to receive, from a terminal device, input values for each of a plurality of setting items, the plurality of setting items including a plurality of related setting items that are related to each other and concern network settings; a first determining unit (S220, S330, S420) that is configured to determine whether the input values, received for the related setting items, that are related to each other, are compatible; and a sending unit that is configured to send, to the terminal device, error data indicating an error screen when the input values received for the related setting items are determined to be incompatible, the error screen showing that at least one input value among the plurality of input values has an error; wherein one of: the communication device further comprises a first storing unit that is configured to store reference values corresponding to the plurality of related setting items, and the first determining unit determines that the input values received for the plurality of related setting items are incompatible when the input values received for the plurality of related setting items do not match the reference values; and the communication device further comprises a verifying unit that is configured to verify that one input value among the input values received for the related setting items falls within a range that is defined by another input value among the input values for the related setting items, and the first determining unit determines that the input values received for the plurality of related setting items are incompatible when the one input value does not fall within the range. the communication device further comprises a first storing unit that is configured to store reference values corresponding to the plurality of related setting items, and the first determining unit determines that the input values received for the plurality of related setting items are incompatible when the input values received for the plurality of related setting items do not match the reference values; and the communication device further comprises a verifying unit that is configured to verify that one input value among the input values received for the related setting items falls within a range that is defined by another input value among the input values for the related setting items, and the first determining unit determines that the input values received for the plurality of related setting items are incompatible when the one input value does not fall within the range.