Disclosed is a catalyst application solution for plating an insulating portion of an object to be plated that comprises the insulating portion. The catalyst application solution is characterized by containing a water-soluble palladium compound, a reducer, a dispersant, catechol, a copper antioxidant and a buffering agent, and by having a pH of not less than 4. When the catalyst application solution is compared with a Pd—Sn colloidal solution, the catalyst application solution has the following advantages: since the catalyst application solution is a colloidal solution of Pd only that does not contain Sn, a pre-dip process and an Sn removal process are unnecessary and thus the catalyst application process can be simplified; since the catalyst application solution has a pH of not less than 4, haloing does not occur; and since the catalyst application solution is in a reducing atmosphere due to the reducer contained therein, a copper surface is not oxidized and no copper dissolution occurs, thereby causing no palladium displacement reaction.