1. An expression processing device comprising: an input unit; a display; and a processor, wherein the processor is configured to perform processes comprising: inputting an expression in response to a user's operation on the input unit; detecting a plurality of variables included in the input expression, among a plurality of variables which are usable in expressions; extracting one or more of a plurality of types of setting data, as setting data essential for calculating the expression, from a memory which stores the plurality of types of setting data relative to expression calculation display; and outputting one or more data items of: the input expression, variable values associated with the detected variables, and the extracted one or more of the plurality of types of setting data, as information for an image generating apparatus outside of the expression processing device to generate an image for external display based on the one or more data items.