An annular switch (SW) for detecting contact is provided on an operating lever (R6), and when the annular switch detects contact, an operation screen (104) pre-associated with the annular switch (SW) is displayed on a display (104) screen of a display unit (104). Operation mode images representing functions included in an operation subject are displayed on the display screen of the display unit in association with a rotation direction and a sliding direction of the annular switch (SW). A function is selected by rotating and sliding the annular switch, and the selected function is executed when the annular switch (SW) ceases to detect contact.