In this article, a force microscope using a twin‐path (common‐path) laser interferometer is presented. The interferometer was developed for the displacement detection of a small cantilever. Since the two interfering beams were very close to each other, the perturbation caused by the environmental disturbances were minimized. The optical path difference between the two beams was easily adjusted by the moire effect of the gratings. The vibrational amplitude of 10−3nm was measured under the resonance conditions of the tungsten lever. The drift rate of the interference signal was less than 10−3nm/s. An etched‐resist coated with thin gold film was imaged by using electrostatic forces under the conditions of ac mode operation.