To provide a drop forming device and its method with which such a suitable size drop as to reach alveolus in the case of a medication to lung of human is formed and a good thermal efficiency is obtained.

A liquid medicine on a surface of a thermal converter (34) is vaporized to generate a bubble by instantaneously heating the liquid medicine filled in a chamber (32) using the thermal converter (34). The liquid in the chamber (32) is pushed out through an orifice (24) by expanding the bubble. The liquid medicine that is discharged from the chamber (32) that is formed to have a specified value of thickness of the chamber (32) against the square root of the area of the thermal converter disperses as many drops with small diameter.