To improve the spray precision of a nebulizer used in spraying treatment to introduce narcotic or the like of regulated dose into inspired gas fed to a patient by making the time without spray measurable by providing a sonar unit for obtaining the position information of the upper boundary surface of a spray chamber.

This ultrasonic nebulizer 1 is provided with an ultrasonic oscillator 2 such as piezoelectric transducer in a water chamber 3, and contains liquid 5 for spraying in a spray chamber 4 on the water chamber 3. Spray liquid is produced on the upper boundary surface 6 of the liquid 5 by the action of the ultrasonic oscillator 2. The spray liquid is added to the inspired gas which is introduced from an inlet 7 and discharged from an outlet 8. At that time, the position information of the upper boundary surface 6 is measured by a sonar detecting means 11 to output and receive sonar pulses 13. The information about dose is obtained from the measurement result, and dose regulation is made by controlling an oscillator driving means 10 by a control unit 12.