PURPOSE: To obtain a thawer, having an ultrasonic generating part contained in a special case and a thawing vessel mounted on the case through engaging tools and capable of rapidly thawing a material to be thawed in the thawing vessel without boiling the peripheral part.

CONSTITUTION: A downward protruding part 4 is fixed to the undersurface of a top plate 6 supported by legs 8 and an ultrasonic wave generator 11 and an ultrasonic vibrator 13 are provided in the interior of the container 5. The ultrasonic vibrator 13 is fixed to the inside of the downward protruding part 4. A thawing vessel 1 is engaged with the container 5 through engaging tools 9 attached thereto. Water 2 is placed in the thawing vessel 1 and a material 3 to be thawed is wrapped in a bag, such as polyethylene, and placed in the water.