To provide a knuckle bracket manufacturing method capable of omitting a straightening step of straightening the flatness, and manufacturing a knuckle bracket at low cost.

In the manufacturing method of the knuckle bracket 1, a substantially cylindrical bracket body 3 to hold an outer shell 2 and a pair of outer brackets 4 protruded horizontally from the bracket body 3 are formed by folding a plate base material 11, an inner bracket 5 having a substantially U-shaped section is inserted between the outer brackets 4, and after the outer brackets 4 and the inner bracket 5 are joined with each other by the projection welding, mounting holes 6 are formed in the outer brackets 4 and the inner bracket 5 so as to pass through the brackets 4, 5. A portion of the base material 11 to form the mounting holes 6 therein before folding is subjected to the brittleness treatment 12.