PURPOSE: To prevent the lime wash of concrete from entering the gaps between a preset surface for an insert retainer and the surface of a formwork without using any excessive force or process, even if such gaps are formed, in a method wherein a projection from the insert retainer is fitted into its preformed mating hole of the formwork to set an insert in the formwork in order to produce the concrete having the insert embedded therein.

CONSTITUTION: The outer peripheral edge 17 of a preset formwork surface 12 which an insert retainer 10 contacts is stretched thinly in a skirt form in the direction of a formwork to make up a shielding membrane 50. When the insert retainer 10 is set in the formwork, since the entry of the lime wash of concrete into the gaps between the formwork surface and the preset surface 12 can be prevented by the shielding membrane 50, even if such gaps are formed, a plug part 11 can be easily removed without being caught in a concrete article. A cut projection 20 is prevented from clogging up the preset form hole by the lime wash of the concrete.