To provide a method for manufacturing a resin ball capable of molding balls having various weights within a predetermined range while suppressing a production cost.

In the method for manufacturing the resin ball by injecting a foamable resin material in a mold comprising a fixed mold 4 and a movable mold 5 to mold a ball for ground golf or park golf while foaming the same, the foaming amount of the foamable resin material injected in the cavity of the mold is arbitrarily adjusted to obtain a ball having a desired weight.