PURPOSE: To cut off efficiently, and contrive an improvement in working environment and saving of a material, by a method wherein an injection molded product is mounted so that the surface of the injection molded product where a sprue is left behind and a saw blade form a little tilting angle, the injection molded product and saw blade are moved relatively while holding the tilting angle and the sprue is cut off.

CONSTITUTION: At the time of mounting of an injection molded product 1 on a cutting device 3, a sprue 2 left behind on the injection molded product 1 is inserted into a table 31 through a hole of the table 31 so that the root of the sprue hits the tip of a saw blade 34. Then the bottom of a flange part 12 of the injection molded product 1 is made to run along the top of a slope rest 32 so that the bottom of the flange part 12 and the saw blade 34 form a little tilting angle. Then a switch of a motor 33 is turned ON, the saw blade 34 is turned and the sprue 2 is cut off while moving the injection molded product 1 obliquely upward long the sloped rest 32 by hand. With this construction, the sprue 2 can be removed from the injection molded product 1 in a short time. Then since the sprue 2 is left behind as a lump even after removal of the sprue 2, working environment is improved and even the resin left behind can be reused.