an air purifier includes a main body defining an air passage therein to allow sucked air to pass therethrough prior to being discharged , and a first filter installed in the main body to be switched between a closed state and an open state . the first filter removes contaminants from the sucked air in the closed state , and allows the sucked air to pass through the air passage in the open state . the air purifier may include a main body to suck and discharge air , with a bypass passage formed in the main body so that the bypass passage is opened or closed by a door , and a first filter installed in the main body . the sucked air passes through the first filter prior to being discharged when the door is closed , and passes through the bypass passage prior to being discharged when the door is opened .