To enhance productivity without being affected by atmospheric temp. while producing a uniform concrete block by providing a heating device part to the under side of a vertical panel part form and providing a pipe piercing part mold on the side of the inclined bottom panel part box frame of the pipe fitting part molds provided to a part on both sides of the form in a projected state.

A heating device part 7 having a heat insulating material executed on the rear surface and side surfaces thereof is provided to the underside of a vertical panel part form 2 and internally heated to heat the rear surface of the vertical panel part form 2, the side surfaces and rear surface of a reinforcing rib form 4 and the side surfaces of an inclined bottom panel part box frame 3. Circular pipe fitting part molds 5 about 1/4 in the vertical cross section thereof are provided in a projected state at height equal to or less than the thickness of a vertical panel part 8 in order to form drain pipe fitting recessed parts after molding to a part of both side edges of the vertical panel part form 2 in the longitudinal direction of the form 2. A pipe piercing part mold 6 having an almost semicircular cross section is provided at height equal to or more than the thickness of the vertical panel part 8 in order to mold a pipe outlet fitting recessed part after molding on the side of the inclined bottom panel part form 3 of the pipe fitting part mold 5 in the thickness direction of the mold.