To provide a method for manufacturing a ball nut 3b, capable of improving roundness of finishing of an outer peripheral surface while suppressing increase in manufacturing costs.

In an inner peripheral surface of a ball nut 3b, an outer diameter side ball screw groove 6b is formed by turning in a part excluding both axial ends. Then, chamfered parts 11c and 11c are formed on inner peripheral edges of both axial ends of the ball nut 3b. Then, while rotating the ball nut 3b by abutting suppressing fixtures on both of the chamfered parts 11c and 11c, finishing is applied on the outer peripheral surface of the ball nut 3b.