To provide an asphalt modifier acting as a binder instead of a modifying polymer in order to modify asphalt including regenerated aggregate.

An asphalt modifier improves physical properties of asphalt up to a similar level as new asphalt by adding to regenerated asphalt, a solid obtained by separating a liquid component from a resinous polymer in production of 2-mercaptobenzothiazole. A method for modifying asphalt comprises adding the asphalt modifier to polymer-modified asphalt and regenerated aggregate.