It is intended to, in a horizontal dry mill, prevent blow-up and adhesion of a raw material, etc., to a raw material input section. In a horizontal dry mill (10) of the present invention, a diameter of a raw material supply section (13) provided in a grinding tank (14) is set to be less than a diameter of a grinding chamber (12). Further, a diameter of a mechanical thrust generating device of the raw material supply section (13) is set to a small value according to the diameter of the raw material supply section. Furthermore, a gap (e1) between an outside dimension of a screw (26) as the mechanical thrust generating device and an inner diameter of the grinding tank (14) in the raw material supply section (13) is set between 0.5 mm and ⅓ of a diameter of each grinding medium M.