The present invention provides a photocatalyst sterilizer (200) which draws thereinto water, contained in a water tank (120) and polluted by bacilli and various organic substances, regardless of a water level in the water tank (120) and sterilizes the polluted water using violet rays and through a photocatalyst reaction, thus enhancing a sterilizing ability thereof, and which is easily installed and efficiently used in various appliances, which are necessary to execute sterilizing processes, for example, hot and cold water generators, hot and cold water purifiers, tap water purifiers to be directly coupled to faucet pipes, edible water purifiers, and aquariums.