[PROBLEMS] To provide: a method of cleaning an endoscope by which the endoscope can be effectively cleaned while being inhibited from deteriorating and a cleaning apparatus and endoscope-cleaning apparatus. [MEANS FOR SOLVING PROBLEMS] An electrolytic cell (11) can produce from tap water an acidic water having a pH of 2-5 and a residual chlorine concentration of 50-300 ppm. An acidic-water tank (14) can store the acidic water, part of which can be supplied to an acidic-water dilution tank (17) and other part of which can be supplied to a high-concentration-water supply part (20). A diluting-water supply part (16) can supply diluting water to the acidic-water dilution tank (17). In the acidic-water dilution tank (17), diluting water from the diluting-water supply part (16) is added to that part of the acidic water which has been sent from the acidic-water tank (14), whereby a diluted acidic water having a pH of 2.3-5.7 and a residual chlorine concentration of 10-60 ppm can be prepared. The high-concentration-water supply part (20) can feed that other part of the acidic water which has been supplied from the acidic-water tank (14) to the opening of an endoscope channel through a channel connection opening (20c).[PROBLÈMES] élaboration dune méthode efficace de nettoyage dun endoscope évitant sa détérioration et dun appareil de nettoyage à cet effet. [SOLUTIONS] une cellule électrolytique (11) peut produire à partir de leau du robinet une eau acide ayant un pH de 2-5 et une concentration de chlore résiduelle de 50-300 ppm. Un réservoir (14) peut stocker leau acide, dont une partie peut être fournie à un réservoir deau acide diluée (17) et une autre partie peut être fournie à un réservoir deau acide à forte concentration (20). Un dispositif dalimentation (16) peut fournir de leau de dilution au réservoir (17). auquel on ajoute de leau de dilution fournie par le dispositif dalimentation (16) à la partie dleau acide provenant du réservoir (14), ce qui permet dobtenir une e
