A method of attaching a head assembly having an annular hollow boss to an arm having a through hole of a carriage is provided. The head assembly includes a load beam of a head suspension and a base plate fixed to a base part of the load beam. The boss is formed on the base plate. The method includes steps of, inserting the boss into the through hole, thereby setting the head assembly to the arm of the carriage, supplying lubricant along the cylindrical jig to the caulking ball and pushing the caulking ball with the cylindrical jig to pass the caulking ball through an inside of the boss and diametrally expand and plastically deform the boss, thereby fixedly fitting the boss of the head assembly to the through hole of the arm of the carriage. The method causes no deformation of a flange formed on the base plate during caulking and is achievable at low cost.