An air purifier includes a first case and a second case that are insertably coupled such that the second case slides up and down with respect to the first case. The first case may suction air through a suction space provided at a bottom and a plurality of holes formed in a side wall. The second case may include a discharge grill provided at a top end through which air is discharged and a plurality of holes formed in a side wall through which air is suctioned when the second case is moved down to a first position and through which air is discharged when the second case is moved up to a second position. The top discharge grill may be opened and closed. The second case may also include a side discharge portion formed in the side wall above the plurality of holes. The side discharge portion may be opened and closed.