To fix provisionally a pin metal piece easily by a simple operation, simplify the post-processing after finishing a curing process, and enable automation of the process for fixing operations.

Insulator porcelain 11 is turned upside down, and its recess 12 at the rear surface is filled with a specified amount of cement mortar 13. A pin metal piece 14 is inserted in the recess 12, and its tip is pushed into the cement mortar 13 and set in the specified position. In the recess 12, an appropriate amount of ceramic balls 2 are put in around the pin metal piece 14 and held in alignment with the axis, and this is accommodated in a vapor curing chamber while the position of the pin metal piece 14 is fixed provisionally, and the cement mortar 13 is cured with vapor and hardened so that the pin metal piece 14 is secured firmly.