PURPOSE: To efficiently insulate a noise source such as a press machine installed on the floor surface, etc., of a factory without requiring a high ultrasonic wave output so much by surrounding the noise source with an ultrasonic wave which is propagated between an upper top lid plate above the noise source and the mount surface of the noise source.

CONSTITUTION: The upper top lid plate 9 has three-layered structure formed by laminating and joining plate materials 13 and 15 of a sound absorbing material on both the upper and lower sides of a plate material 1 of a sound insulating material, and on the outer peripheral edge part of the upper top lid plate 9, plural ultrasonic wave generating devices 17 are fixed and installed facedown along the outer peripheral edge so that the outer peripheral edge part is surrounded. An acoustic lens 21 which converges the ultrasonic waves radiated to the floor surface by ultrasonic wave generating devices 17 is suspended and mounted on the upper top lid plate 9. Further, an ultrasonic wave reflecting member 23 is slantingly arranged on the floor surface 1 that the ultrasonic waves from the ultrasonic wave generating devices 17 reach. Consequently, a sound insulating elastic wave curtain is formed of the ultrasonic waves surrounding the noise source 5 between the upper top lid plate 9 and factory floor surface 1.