The results of fundamental experiments and trial device for developing a multi-aperture-membrane ultrasonic atomizer are described. The trial device is manufactured with a bender bimorph vibrator, which is composed of a pair of a thin steel membrane and a circular ring piezoelectric element. The authors use three kinds of membranes of 50 μm in thickness with 61 pinholes formed by photo etching technique. Apertures of the pinholes are 170, 300 and 450 μm, respectively. Particles larger than 100 μm are counted in proportion to pinhole aperture.