To assure a good visual field as glass for viewing outside and to enhance the degree of freedom in use by mounting an ultrasonic vibrator transducer which generates ultrasonic vibration in part of the glass for viewing outside and setting the driving frequency of this ultrasonic vibrator transducer at the natural resonance frequency of the glass for viewing outside.

The ultrasonic vibrator transducer 2 consists of the ultrasonic vibrator transducer which generates the ultrasonic vibration of the driving frequency set at the natural resonance frequency (determined from magnitude and shape) of transverse waves possessed by a windshield 5 as the glass for checking outside, i.e., the ultrasonic vibration of the driving frequency matched with the vibration mode at the natural resonance frequency possessed by the windshield 5. This ultrasonic vibrator transducer 2 is mounted at part of the rear surface of the windshield 5. As a result, when the driving frequency is impressed from the natural resonance frequency on the windshield 5, the windshield 5 curves and vibrates and the loop and node of the vibration meeting the driving frequency are generated over the entire part of the windshield 5.