An air purifier includes a bell-mouth having an enhanced structure to prevent an increase of noise at a particular frequency when air flows into the blowing fan through the bell-mouth. The air purifier includes a housing, a filter unit and a blowing fan placed inside the housing, and a bell-mouth placed toward an intake side of the blowing fan. The bell-mouth includes an inlet port formed at a center of the bell-mouth, a flow guide extending from a periphery of the inlet port toward the blowing fan, and a flat section positioned to discontinue the flow guide to increase a distance between the blowing fan and the bell-mouth. The flat section is formed at the section in the range of about 240°˜330° with respect to a starting point of a scroll inside the bell-mouth. The flat section may have a saw-tooth shape to effectively distribute air passing therethrough.