A nozzle apparatus of a dishwasher including a washing nozzle configured to inject washing water onto targets to be washed, a water supply passage part for allowing the flow of washing water supplied to the washing nozzle, a drain passage part for allowing the flow of washing water to be drained, and a siphon preventing portion configured to prevent a siphon phenomenon from occurring on the drain passage part, whereby a space required for configuring a drain passage and a siphon phenomenon preventing structure can be minimized so as to maintain the dishwasher in a compact size and improve the space utilization.