The present invention aims to provide a surface modification method for a rubber vulcanizate or a thermoplastic elastomer, which can impart excellent sliding properties and excellent durability against repeated sliding motion and can allow the surface to maintain the sealing properties, without using expensive self-lubricating plastics. The present invention relates to a surface modification method for modifying a rubber vulcanizate or a thermoplastic elastomer as an object to be modified, the method including: step 1 of forming polymerization initiation points on the object to be modified; step 2 of radically polymerizing a monomer, starting from the polymerization initiation points, by irradiation with LED light at 300 nm to 400 nm to grow polymer chains on a surface of the object to be modified; and step 3 of esterifying, transesterifying or amidating side chains of the polymer chains.