A scanning endoscope system includes an endoscope that includes an illumination fiber that is configured to guide illumination light for illuminating a subject and to emit the illumination light from an emitting end, and an actuator section that is configured to swing the emitting end of the illumination fiber according to a voltage or a current of an electrical signal that is applied to cause the illumination light to scan the subject, and a driver unit configured to apply, to the actuator section, the electrical signal that takes, as a drive frequency, a frequency at which an amount of change in amplitude at a time of swinging of the emitting end of the illumination fiber is at or below a predetermined value even when frequency characteristics of the amplitude are changed due to a change in a use condition of the endoscope.