To provide a cross flow fan capable of restraining the decrease in the amount of wind.

A circular insertion hole 7 in which an impeller 3 is to be inserted is opened on one side plate surface 2C of a casing 2, and an annular clearance 11 is generated between the insertion hole 7 and the end plate 3a of the impeller 3 after the impeller 3 is inserted. A wind leakage preventing cover 5 is cylindrically erected on the side plate surface 2C of the casing 2 having the insertion hole 7 and on the periphery of the insertion hole 7, the lower end is bonded to the side plate surface 2C, and the upper end is bonded to a flange part 9 of a motor 4. Since the periphery of the insertion hole 7 is covered with the wind leakage preventing cover 5, wind leakage from the clearance 11 can be prevented when the impeller 3 is rotated. As a result, since pressure fluctuation generated in leaking of wind is eliminated, eccentric vortex generated in the casing 2 is stabilized, and the flow of air passing through the impeller 3 is stabilized with the generation of the eccentric vortex.