To provide a method for producing an asphalt modifier capable of making the balance among prescribed properties other than the suppression of separation compatible on a high order without causing the separation even in long-term storage.

This method for producing an asphalt modifier comprises kneading a thermoplastic elastomer with carbon black and an oil. The kneading temperature is 80-200°C and the kneading time is 1-30 min. The shear rate at the time of kneading is 50-800 (s-1) and the shear energy acting on the carbon black based on 1 cm3 of the carbon black at the time of kneading is 200-3,000 (J/cm3).