Provided are a method for generating mechanical and electrochemical cavitation, a method for changing the geometric shape and the electrochemical properties of a surface of a substance, a method for peeling off a rare metal using the generated mechanical and electrochemical cavitation, a mechanical and electrochemical cavitation generator, and a method for generating a nuclear fusion reaction of deuterium. In the method for generating mechanical and electrochemical cavitation, a water jet is jetted from a jetting nozzle immersed in water, and flow cavitation generated by the jetting of the water jet is irradiated with an ultrasonic wave to generate cavitation MFC having both a functional effect and an electrochemical effect.