An instrument executes: generating pieces of setting information for assigning operation functions to respective operating units; assigning the operation functions to the respective operating units based on first one of the pieces of setting information; setting one of the operating units as a setting operating unit to which an operation function for switching the first one of the pieces of setting information to second one of the pieces of the setting information assigned to the setting operating unit is assigned; changing, upon a first operation of the setting operating unit, the operation functions of the operating units based on the second one of the setting information and inhibiting a change in the operation function assigned to the setting operating unit; and returning, upon a second operation of the setting operating unit after the first operation, the operation functions of the operating units to those assigned before the first operation.