To provide a form which serves also as a spacer which is capable of joining PC posts with each other easily.

A plurality of weir boards 6a and 6b are set up windingly in a joining area of upper and lower PC posts 1 and 2 in such a fashion that they may surround the joining area, thereby closing up a clearance between the PC posts 1 and 2 while a plurality of fixing areas 6d and 6e are provided, which are projectingly mounted on the weir boards 6a and 6b and bolted with the outside surfaces 1a and 1b and 2 and 2b of the PC posts 1 and 2 respectively and which are designed to fix the weir boards 6a and 6b with the outside surfaces 1a and 1b of the PC posts 1 and the outside surfaces 2a and 2b of the PC post 2, thereby constituting this form which serves as a spacer.