A cross flow having a volute is disclosed which is less noisy during its operation. A volute-portion starting radius which is the length of a segment O-F1 at a volute-portion starting point F1 is R1; a maximum volute radius which is the length of a segment O-F2 at the outlet portion starting point F2 is RM; a maximum volute angle which is an angle formed by the segment O-F2 and O-F1 is PROPORTIONAL M; a point on the volute portion having a distance to the center O of the rotating shaft is RJ=(R1+RM)/2; an angle PROPORTIONAL J is formed by a segment connecting that point and the center 0 of the rotating shaft; the segment O-F1 is PROPORTIONAL M/2 (=F1-O-FJ); a volute portion of a scroll casing is formed into a circular arc such that R1<RJ<RM, and the circular arc passes through the points F1, FJ, and F2.
