A function execution method includes a selection step in which the a user is encouraged to select multiple shortcut functions to be executed subsequently from among a registered plurality shortcut functions each of which is configured to be executed with user of a preliminarily setting value necessary for executing the particular function, a continuous execution registration step in which a continuous execution function configured to execute the multiple shortcut functions selected in the selection step such that the multiple functions are executed in accordance with a particular order, a displaying step in which a continuous execution key corresponding to the continuous execution functions registered in the continuous execution registration step, and a continuous execution step in which, when the continuous execution key displayed by the displaying step is selected, the controller executes the multiple shortcut functions constituting the continuous execution function in accordance with the execution order.