PURPOSE: To thaw a material at a low temperature uniformly in a short time, by applying ultrasonic energy to the material placed in a liquid medium in a container with an ultrasonic generator.

CONSTITUTION: The material 3 is exposed to ultrasonic waves at a frequency of about 100kHz generated by the unit 6, using the solvent 7 capable of transmitting the waves. The material 3 is thawed from the surface to the interior in order. The thawed part will absorb little energy, and the thawing is effected uniformly with the energy concentrated in the frozen part.