PURPOSE: To develop an ultrasonic wave generator for surface treatment of a substrate which has extremely high surface treatment effect by washing liquid or liquid chemicals and by which bubbles generated on a substrate are rapidly removed and by which dust being present on a recessed and projection part finely machined on the surface side of the substrate is removed on the surface side thereof.

CONSTITUTION: An ultrasonic wave generator Z for surface treatment of a substrate arranged adjacent to at least one surface of a substrate to be surface- treated by a surface treating liquid L such as washing liquid and liquid chemicals and for applying ultrasonic waved to the treating liquid L flowing between the generator and the substrate to treat the surface of the substrate is provided. It is constituted of a vibrator 3 for generating ultrasonic waves and a housing 4 for housing the vibrator 3. An ultrasonic wave transfer part 11 is formed between the vibrator 3 and an opposite surface 12 opposite to the substrate of the housing 4.