PURPOSE: To enable all fan blades to be uniformly formed in a mold for forming a lateral flow fan comprising of a side plate member formed integrally with a plurality of fan blades by forming at least one of the outer and inner molds of a plurality of mold pieces.

CONSTITUTION: Three right side cavities are defined by the outer mold 5 and the inner mold 6 and the left side cavity by another second inner mold 7 and second outer mold 8. The outer mold 5 is withdrawn in the direction of arrow A and the inner mold 6 in the direction of arrow B. Also, the second inner mold 7 is withdrawn in the direction of arrow C and the second outer mold 8 in the direction of arrow D. Thus, since a fan blade having a regular stream line shape can be formed without being restrained with respect to the withdrawing direction, noises are reduced and wind amount can be increased to improve fan efficiency.