An ultrasonic wave nebulizer for converting water or liquid to mist has a disc-shaped piezoelectric vibrator (1) which has a pair of surfaces one of which is defined as an operation surface. A mesh (3) is located close to said operation surface so that a gap (G) or a thin water or liquid film is defined between the mesh and the operation surface. The gap spacing is smaller than the diameter of water drop which is composed by surface tension of water when no mesh were located. Upon excitation of the vibrator with high frequency, the water film is converted to mist. Fresh water is supplied in said gap spacing through capillarity. The exciting frequency is almost the same as the resonant frequency of the vibrator. The present nebulizer is useful for a small atomizer which operates with small power consumption.