To easily design a fan by inputting necessary performance from a menu displayed on a display device.

A display device 5 is provided, the fan request performance, namely, the specifications of the wind capacity Q, the head H, and the noise level LA are input from an input unit 1, the optimum fan type is determined by calculating various characteristic values on the basis of the fan specification, and the design data of an impeller and a casing are calculated by using the date classified and stored in a data storing part 3 for each type of fan by forming the design data of a normal fan into the sequence. The approximate dimension drawing drawn on the basis of the values is output from an output unit 4.