To more securely remove metal stuck to the inner wall of an injection sleeve in an injection molding machine.

At the upper part on the side opposite to a die 30 in an injection sleeve 40 which is connected to the die 30 and stores molten metal, two air injection holes 44a, 44b having an angle of 30° to the direction on the side of the die 30 toward the inside and further having an angle of 30° to the inner wall of the injection sleeve 40 are formed, and, after metal parts molded by injection molding are taken out, and, in a state where the die 30 is opened, air is injected from the air injection holes 44a, 44b into the injection sleeve 40. The injected air is made into a rotating flow with strong force flowing toward the side of the die 30 as a whole within the injection sleeve 40, peels metal stuck to the inner wall of the injection sleeve 40, and exhausts the same from the side of the die 30 to the outside. In this way, the metal stuck to the inner wall of the injection sleeve 40 can be more securely removed.