The present invention is directed to a method for replacing a nucleus pulposus in an intervertebral disk, which method includes: providing a spinal intervertebral disk replacement molded-dry-product for nucleus pulposus including a polyvinylalcohol gel having a percentage of saturated water content of 18 to 50 wt % before irradiation and being irradiated with γ ray at an intensity of 20 to 100 kGy; and inserting the spinal intervertebral disk replacement molded-dry-product for nucleus pulposus into a prosthetic space inside an anulus fibrosus through an incision opening of the anulus fibrosus, wherein the molded-dry-product changes its shape into an almost cylindrical or almost elliptically cylindrical shape so that a hollow region comes into existence at a shape deformation rate of 150 vol % or more and at a volume swelling ratio of 135 vol % or less by water absorption.