A chemical supply system comprises, as principal elements, a chemical storage tank in which a liquid chemical for cleaning is stored in the state of its formulated concentrate, a chemical supply apparatus connected to the chemical storage tank for positively performing chemical supply, a piping system connected to the chemical supply apparatus to form a supply flow passage that is a passage for ultrapure water which the liquid chemical is to be mixed with, a pair of discharge nozzles disposed at end portions of the piping system so as to oppose surfaces of a wafer set in a cleaning chamber to supply a cleaning liquid onto the surfaces. Thereby, remarkable miniaturization/simplification of a cleaning liquid supply system including chemical tanks is intended, it is made possible easily and rapidly to compound and supply a cleaning liquid at an accurate chemical concentration, and particles or the like being generated and mixing in a cleaning liquid, are suppressed to the extremity.