Provided are a nitrite-type nitrification carrier and a method for producing the same and a method and an apparatus for removing nitrogen using the same, in which the quantity of organic matter to be added can be substantially reduced to reduce running cost. A method for producing a nitrite-type nitrification carrier in which ammonia-oxidizing bacteria for nitrifying ammonium to nitrite is preferentially accumulated comprises the steps of: entrapping and immobilizing any sludge selected from sediment from a lake, a river or the sea, soil from the surface of the earth, or activated sludge from a sewage-treatment plant into a monomer or a prepolymer for immobilizing microorganisms; and then subjecting the entrapped and immobilized sludge to heat treatment at 30 to 80.degree. C.