A defoaming method capable of destroying foams generated when a container is filled with drink, or the like, efficiently at a high speed and destroying foams effectively even in the case of a container having a narrow mouth. Liquid surface (6) in a container (1) is irradiated with pulse-like light (2) and a pulse-like sound wave (8) is generated from an irradiated point (7) as a sound source. The pulse-like sound wave thus generated propagates from the sound source as a strong spherical wave to reach a bubble (9) and to destroy the bubble. It can also destroy a bubble located at a place remote from the optical path quickly, thus destroying bubbles efficiently at a high speed. Alternatively, pulse-like light is condensed at a gas portion above the liquid surface and the bubbles can be destroyed with a shock wave generated by breakdown phenomenon.