To provide an injection-forming apparatus in which it can be prevented that a material made to a low viscosity state stays in a gap between mating surfaces.

Molten magnesium alloy injected into a gap A between the second side surface 14 of a first mold member 10 and the second side surface 24 of a second mold member 20 is passed through a gap between the second lower surface 21 of the first mold member and the second lower surface 21 of the second mold member 20 and successively passed through a gap between the first side surface 13 of the first mold member and the first side surface 23 of the second mold member, and tends to invade into a gap between the first bottom surface 11 of the first mold memeber and the first bottom surface 21 of the second mold member. However, this molten alloy is discharged to the outside through a drain hole 15 made to a larger diameter as going to the lower part.