PURPOSE: To prevent stringing and a variation in cutting position when a resin is cut at a gate by a method wherein a tip end part of a pin is inserted to the gate from the opposite side of a product surface provided with the gate, and the tip end of the pin is made acute to form a minimum cross sectional area part on a cutting position.

CONSTITUTION: A gate 1 is provided on a product surface F of an injection mold 5. A pin 2 is disposed in the gate 1 from the opposite side of the product surface F. The pin 2 comes close to the product surface F to be inserted to the gate 1. The tip end of the pin 2 is made acute. A minimum cross sectional area part S is formed on the side opposite to the gate. Thus, a resin can be cut on the product side. In cutting, the resin is acceleratedly set at the minimum cross sectional area part S, thus being prevented from stringing in a melting state. Furthermore, a variation in cutting position is also prevented. In this manner, there is no possibility that the resin may remain in the gate under the product surface. Therefore, the need for forming a draft in the gate of the mold is eliminated, and the metallic mold can be easily machined.