Provided is a friction drive actuator that is resistant to contamination of, for example, extraneous matter. An ultrasonic actuator according to an aspect of the present invention drives a columnar insertion section and includes a columnar vibrating body (40), whose distal end is pressed against a side surface of the insertion section, and a piezoelectric element (44), an upper electrode (44a), and a lower electrode (44b) that are provided at one side surface of the vibrating body.