The present invention is directed to manufacturing methods of electrostatic type MEMS devices. The manufacturing method of the present invention includes the steps of forming a substrate side electrode on a substrate, forming a fluid film before or after forming a sacrificial layer, further forming a beam having a driving side electrode on a planarized surface of the fluid film, and finally, removing the sacrificial layer. Furthermore, performing the foregoing method planarizes the surface of a driving side electrode, reduces fluctuations in the shape of a beam, and improves the performance and the uniformity of the MEMS device.