A backflow prevention device includes a reservoir defining a space to store dregs therein, an inflow unit having an inlet hole formed therein and defining a path to allow the dregs to move through the inlet hole into the reservoir, a discharge unit having an outlet hole formed therein and defining a path to allow air in the reservoir to be discharged through the outlet hole, and a barrier unit provided in the reservoir to change a flow direction of at least either of the dregs and the air at least once and thereby prevent the dregs from flowing into the discharge unit.
