A carbon black is provided which is useful as an electrocatalyst carrier. The carbon black has a DBP oil absorption of 170 to 300 cm.sup.3/100 g, a specific surface area as measured by a BET method of 250 to 400 m.sup.2/g, a primary particle diameter value of 10 to 17 nm, and a total volume of open pores at the surface which have a pore radius of 10 to 30 nm of 0.40 to 2.0 cm.sup.3/g. The electrocatalyst can be used in electrochemical devices such as solid polymer electrolyte fuel cells.