A syringe forming mold in which a channel of cooling water for cooling a core cylinder is disposed close to a cavity space to thereby ensure a satisfactory circulating flow rate of cooling water. Slide cores (5,5) are placed at a position protruding from the circumferential plane of core cylinder (2) by penetration manipulation of slide core manipulation jig (4) along the axial direction of the core cylinder (2). While cooling the core cylinder (2) by cooling water, a molten resin is injected into cavity space (C) around the core cylinder (2). Thus, there is formed a syringe of two-drug mixing type injector furnished at its inner circumferential surface with a communication groove for mixing two drugs. As the cooling water channel is provided in partition around a jig accommodating space within the core cylinder (2), the channel lies close to the cavity space and the section of the channel can be made large to thereby ensure a satisfactory circulating flow rate of cooling water. Therefore, forming failure due to unsatisfactory cooling of the core cylinder (2) can be prevented.
