A surface treatment agent which is a water-repellent agent, includes (1) a fluorine-free block copolymer, and (2) a liquid medium which is an organic solvent, water, or a mixture of water and an organic solvent. The non-fluorinated block copolymer includes at least one block segment (A) which includes a repeating unit formed from one or more types of acrylic monomer having a long-chain hydrocarbon group containing 12-40 carbon atoms. The non-fluorinated block copolymer preferably contains a segment (B) constituted by at least one of: (B1) a block segment including a repeating unit, different from that of segment (A), that is formed from an acrylic monomer having a long-chain hydrocarbon group including 12-40 carbon atoms; (B2) a block segment including a repeating unit formed from an acrylic monomer not having a long-chain hydrocarbon group; and (B3) a random segment formed from at least two types of acrylic monomers.