An object of the present invention is to provide a low pressure loss filter having a high dust- and dirt-collecting capability and excellent workability and sustainability of collecting capability. The filter of the present invention is a filter having air channels formed using an electret sheet; a porosity of the electret sheet being from 1 to 70%; an air channel cross-sectional ratio of the filter being from 10 to 99%; and a volume charge density of the filter being from 10 to 5000 nC/cm3.