A method of manufacturing a yoke of an electric rotary machine is disclosed. The manufacturing method includes providing a cutout steel plate having one end formed with a plurality of concave portions and the other end formed with a plurality of protrusions, rolling the cutout steel plate into a cylindrical shape until a distal end of each protrusion faces the inlet of each concave portion, inserting the protrusions into the concave portions, respectively, in a circumferential direction, and conducting punch-caulking press on each protrusion at near-wall areas on both sides thereof in close proximity to indents of each concave portion to form localized expanding portions at the near-wall areas on both sides of each protrusion while causing the localized expanding portions to flow axially outward to be fitted into the indents of each concave portion, respectively.