PURPOSE: To ensure that a comfortable space can be created without causing an unpleasant feeling to a user due to a noise during operation regardless of a place and an environment where an air purifier is used.

CONSTITUTION: This air purifier consists of a fan motor 1 which generates an air current, a means 2 of switching a motor for driving the fan motor 1, a means of controlling 3 for outputting a signal to the means 2, a microphone 4 which detects an ambient sound, an audible band filter 5 which extracts an audible band frequency sound from an output from the microphone 4, a means of comparison 6 which compares an output from the audible band filter 5 with plural values, and a variable means of comparison value which varies an output value to the means 6 by an output from the means 3.