Disclosed is a technique of achieving weight reduction of a forged rotary body while improving productivity of the forged rotary body. Temporary center holes are set for each of two or more samples extracted from one forging lot of a plurality of forged rotary bodies produced within a time period after a die misalignment adjustment through before a next die misalignment adjustment. Then, a virtual final shape of each of the samples is simulated on an assumption that machining is performed on the basis of the temporary center holes, and a rotational imbalance amount is calculated. Then, an average value of the rotational imbalance amounts in all of the samples in the same forging lot is calculated, and center-hole positions which allow the average value to become zero are set as center hole machining positions for all of the forged rotary bodies in a corresponding forging lot.