The present disclosure relates to a drainage device and a dishwasher having the same. The drainage device includes a drain pump including a drain port for discharging water, a drain pipe guiding discharge of water discharged from the drain pump, an air chamber in which the drain pump is connected to an upper portion thereof and the drain pipe is connected to a lower portion thereof, and an air pump configured to inject air into the air chamber, thereby more surely blocking the backflow of water to the drain pump by air injected into the air chamber through the air pump.