An ultrasonic wave nebulizer for converting water or liquid to mist has a disc-shaped piezoelectric vibrator (TD) which has a pair of surfaces one of which is defined as an operation surface. A thin plate (21) having a plurality of small holes or mesh is located close to said operation surface so that a gap 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 power, the water film is converted to mist. The exciting frequency is almost the same as the resonant frequency of the vibrator. Said high frequency power is intermittent having duty ratio (D ON /D) in the range from 10 % to 70 % so that instantaneous exciting power is high to facilitate water to mist conversion while average power is low to keep temperature at the operation surface low. The present nebulizer has many applications, including medical inhaler, a toy which generates pseudo smoke et al.