Asphalt modifier foamed for road pavement and its preparation method

Provided are a foam for modifying asphalt which is increased in the amount of a branched styrene-butadiene-styrene block copolymer, is minimized in the amount of a tackifier resin and is lowered in manufacturing cost, and a method for preparing the foam. The foam comprises 60-100 parts by weight of a branched styrene-butadiene-styrene block copolymer having a weight average molecular weight of 50,000-300,000; 0.01-40 parts by weight of a tackifier resin; 0.01-50 parts by weight of a process oil; and 0.01-20 parts by weight of a physical or chemical foaming agent having a foaming temperature of 50-250 deg.C and a gas generation amount of 20-400 mL/g. The method comprises the steps of extruding the foam composition with melting and mixing 100-200 deg.C.