Abstract: A method for disassembling and assembling a mold enables a return pin to be safely attached or detached against an elastic force of the return spring. The fitting length between the return pin and the sliding hole formed in the movable mold plate is so determined that a fitting state of a predetermined length remains between the return pin and the sliding hole when the elastic force of the return spring is released to a practically safe level, and the return pin has, at the end, a threaded hole for fitting an operation male screw to be used for disassembling and assembling of the mold. While the male screw is screwed into the threaded hole through the sliding hole from the fixed side, the male screw is fed to move the return pin in the sliding hole, until the elastic force of the return spring is released to a practically safe level.