A golf ball manufacturing method comprises a step of holding a spew (B) of a seam (C) of a golf ball (G) in a predetermined position, a step of deciding whether the position of the seam (C) is normal, and a step of distinguishing the necessity of the processing of the golf ball based on the decision, and furthermore, a step of processing the seam (C) which removes the spew (B) of the seam (C) and smoothens a removing mark, and the step of processing the seam (C) is constituted by a plurality of stages including cutting and grinding. The processing is carried out at an angle obtained by inclining an angle for processing the seam C in the direction of the flow of a polymer in the seam C. According to the golf ball manufacturing method, the appearance of the seam is very smooth and the performance of the ball can be more uniform.