Abstract: A plurality of recesses, each having a semicircular section, are formed close to each other in the inner surface of a cylindrical housing so that these recesses extend parallel to the axis of the housing. The inner surface of the housing, a portion of a circle which is part of each recess, and the ends of the vanes of a rotor are provided starting from the curvature centers of the semicircular recesses to the axial center of the housing.

Abstract: An opposed type jet mill, in which a discharge pipe for feeding a mixture flow of high speed gas and ground material discharged from a grinding chamber to an airflow classifying chamber is provided nearly at an equal distance from a new raw material accelerating injector and a regrinding raw material accelerating injector disposed on the left and right hands, respectively, of the grinding chamber and at right angles to a common center line of the both injectors, and a coarse grain return pipe for feeding coarse grains separated in said airflow classifying chamber to the regrinding raw material accelerating injector is disposed so that the angle formed between said return pipe and said regrinding raw material accelerating injector may become an acute angle of 60 degrees or less, which jet mill can reduce energy loss of gas flows and yet can achieve micro-fine grinding.