The invention provides a novel pretreatment agent for electroless plating, which can attain high adhesion between insulating resin substrates and plating films, which can suppress the generation of foams in a short time to have high foaming resistance, and which can exhibit high penetrability into insulating resin substrates. The pretreatment agent for electroless plating includes a fluorine compound; a surfactant; and at least one solvent selected from ethylene-based glycol butyl ethers of formula: C4H9-(OC2H4)m-OH where m is an integer of 1 to 4, and propylene-based glycol butyl ethers of formula: C4H9-(OC3H6)n-OH where n is an integer of 1 to 4.