Electrically conductive fiber and brush

A conductive fiber containing carbon black as a main conductive component in a fiber-forming polymer, wherein the carbon black is composed of a mixture of at least two kinds of the following carbon blacks (A) and (B), which is obtained by mixing them at an A/B ratio (by weight) of 90/10 to 10/90:

• (A) A conductive carbon black having an average particle size of 20 to 70 nm and an oil absorption defined in JIS K 5101 of 100 to 600 ml/100 g;
• and
• (B) A conductive carbon black in which the average article size ratio thereof to said conductive carbon black (A) is from 1.1 to 3, and the oil absorption ratio thereof to said conductive carbon black (A) is from 0.9 to 0.2,
• wherein the cross-sectional resistance value is from 108 to 1012 Ω/cm,
• wherein the conductive fiber is a sheath-core type composite fiber, and
• wherein the sheath component contains the mixture of at least two kinds of carbon blacks (A) and (B) in an amount of 10 to 35% by weight.