PURPOSE: To perform various operations necessary for injection molding by a robot whose main body is small, by a method wherein an industrial robot having a running shaft is combined with an injection molding machine.

CONSTITUTION: An injection molding device 1 is constituted of an injection molding machine 2, a robot 3 for taking-out a molded product, a gate-cutting device 4 and a carrying conveyor 5 of the molded product. The injection molding machine 2 is under control of an NC device. In the robot 3, it is provided with a rail 12 and main body 13, a joint of an arm is made capable of performing an up-and-down motion and a base part is made turnable horizontally. In the NC device 16 for the robot 3, an operational program of the robot 3 is stored in the NC device and operation is performed by a start signal and completion signal through the NC device 10 for the injection molding machine. Since the robot 3 can perform positioning by running on the rail, operation can be attained sufficiently even if the arm 14 is short and main body is tiny.