PURPOSE: To easily demold a core-form which molds a recessed groove of a half-precast beam as a concrete product and effectively prevent damage of the core-form.

CONSTITUTION: By pushing up a support beam 22 upward with a hydraulic jack 23, a core-form 13, a half-precast beam 30 molded at its periphery, an outside face form 11 in fast contact with both sides of the half-precast beam, and a bottom face form 12 are floated from a base stage 14. The outside face form 11 and the bottom face form 12 are pulled out from both sides of the half-precast beam 30. After the half-precast beam 30 is suspended by a wire 24 of a crane, the core-form 13 is displaced to the lower part by the hydraulic jack 23. Further, a dolly 21 is moved in the longitudinal direction of the half- precast beam 30, so that the core-form 13 is pulled out from a recessed groove 30a of the half-precast beam 30.