An apparatus washes/disinfects, at a time, a plurality of endoscopes having a plurality of channels with different diameters, and dewaters the channels at a time. For the dewatering, the apparatus includes plural ports for receiving air supply, and a plurality of tubes for connecting between each of the plurality of ports and each of the plurality of channels in each of the plurality of endoscopes. The apparatus also includes an on-off valve for intermittently supply air to the ports, and a control unit for opening/closing the valve a plurality of times at a predetermined ratio. Water droplets remaining in a large-diameter channel are mainly moved by wind pressure of continuously flowing air while the valve is open, and discharged. Water droplets in a smaller-diameter channel are mainly moved by hammer effect of high-pressure air caused while the valve is closed, and discharged. The valve opening/closing is repeated for complete dewatering.