a wet processing device of this invention is comprised of a chemical processing tank to store chemicals for processing the surface of the wafer , a wafer conveyor device to carry the wafer in and out of the interior of the chemical processing tank , and a sensor to determine the amount of air bubbles occurring within the chemical when present within the chemical processing tank and issue a first and a second control signal , and a wash tank to store water for washing the wafer carried out from the chemical processing tank by the wafer conveyor . the rising speed of the wafer conveyor device pulled the wafer up from the chemical processing tank is controlled in response to the first control signal , and the wash tank water fill quantity for supplying water to the wash tank is controlled in response to the second control signal .