To provide a core for forming a through hole in concrete moldings which does not require a troublesome operating step such as an operation to apply a mold lubricant and enhances productivity.

This core for forming a through hole in concrete moldings is introduced into a form 4 finding its way through a pair of openings 41 is the form 4, located opposite to each other across a specified space. Both end parts of the core are made up of a rubber tube 1 retained by both molding frame operating 41, a plug member 2 which blocks the opening on one of the end sides of the rubber tube 1, and a connecting member 3 with an introduction aperture 3b which blocks the opening on the other end side of the rubber tube 1 and introduces a compressed fluid into the rubber tube 1. In addition, a mold lubricating rubber layer 1b comprising a self-lubricating rubber is provided on the surface of an outer periphery where the rubber tube 1 comes into contact with an least, a concrete.