PURPOSE: To comfortably listen to radio or watch TV of a prescribed program without permitting insect pests to come flying near human bodies, as the environment is kept clean, by transmitting the same ultrasonic waves that are oscillated by the natural enemy such as a bat in the form of an electronic sound from the speaker of an electronic appliance such as a TV set, radio, CD player or tape recorder.

CONSTITUTION: On the background of the sound waves 3 from the speaker 2 in a TV set 1 as an electronic appliance, an electronic sound corresponding to the ultrasonic waves emitted by the natural enemy is emitted to repel mosquitoes out of the range of the ultrasonic wave. The sounds of a music program or the like can be listened without any adverse effect, while the insect pests such as mosquitoes are repelled from the range of the ultrasonic wave, as the environment is kept clean without emission of ultraviolet rays with no adverse effect on health.