To obtain a composite magnetic body which is improved in flame retardant properties and furthermore shortened in a kindling time after self- extinguishment, by a method wherein a flame retardant material is completely or partially formed of hydroxide or/and inorganic hydrate.

Soft magnetic powder 3 and a titanate coupling agent are introduced into an agitator and uniformly mixed so as to enable soft magnetic powder 3 to undergo a coupling treatment. Then, soft magnetic powder subjected to a coupling treatment, chlorinated polyethylene 2, magnesium hydroxide 4, bromine polymer flame retardant material, and antimony trioxide are introduced into a pressure kneader and kneaded for obtaining a mixture for a composite magnetic body 1. Then, the mixture is rolled into a sheet-like composite magnetic body 1 by the use of rolls arranged in parallel. Magnesium hydroxide is used as the main component of flame retardant material, and when aluminum hydroxide, calcium sulfate hydrate, zinc borate hydrate or a mixture of them is used, the same manufacturing method is employed.