PURPOSE: To form a sirocco fan having the total length of cross section of a blade longer than pitch of the blades by forming parallel grooves in side direction having the prescribed pitch in longitudinal direction of raw material, shearing at bottom parts of the grooves and forming the blades having the desired shape after executing two forming processes to bending sheared pieces, where one side is bent in the groove and the other side is as it is.

CONSTITUTION: On the strip shaped raw material having calking pieces 4 of the fixed pitch at both side edges, the U shape grooves 2 of the pitch P are formed and sheared at almost center of the bottom thereof, and the one side is made to the bending piece 2a and the other side is as it is 2b. From the 2a and 2b parts, the blades 3 having the desired shape are formed with the two processes to obtain the blades 3 having the length L of cross section longer than the pitch P. Successively, the worked material W having the blades 3 is rolled up to make cylindrical body, and the calking pieces 4 are inserted into inserting holes arranged in circular direction of round shape side plates 5a, 5b. By this method, the sirocco fan having less number of parts and easy to assemble can be obtd.