An endoscope washing and disinfecting apparatus of the present invention includes an air pump supplying a gas to an endoscope channel included by an endoscope, a faucet supplying a liquid into the endoscope channel, a channel connectable to a mouthpiece of the endoscope channel included by the endoscope and supplying at least one of a gas or a liquid to the endoscope channel, and an injector converting the liquid into a liquid droplet, mixing the liquid droplet into the gas flowing in the channel with the size of the liquid droplet changeable, and thereby supplying gas-liquid two-phase flow in which the liquid droplet is mixed at a set ratio into the gas into the endoscope channel through the channel.