An air purifier and a filter cleaner are provided. The filter cleaner is configured to be mounted in an air purifier. The filter cleaner comprises a motor, a cleaning member and a gear mechanism. The motor is configured to drive the gear mechanism to drive a radially outwards facing surface of a cylindrical air filter or a filter holding case past the cleaning member. The air purifier can comprise a polygonal casing and the cylindrical air filter can be located inside the polygonal casing so that a space is formed between the radially outwards facing surface of the cylindrical air filter and the inside corners of the polygonal casing. The filter cleaner can be located in the space between the corner and the filter.