A contact charger for charging a charging target (e.g., a photosensitive member) includes a charging brush to be in contact with the charging target, and auxiliary charging particles to be interposed between the brush and the charging target. The auxiliary charging particle takes an acicular form having an aspect ratio from 2 to 10000, and satisfies a relationship of (L.sup.2/T.ltoreq.200) between a length L (.mu.m) of a long axis of the particle and a thickness of T (deniers) of a brush fiber of the brush.