An actively stabilized interferometer with a constant optical path difference is a key element in long-term astronomical observation, and resolving interference fringe ambiguities is important to produce high-precision results for the long term. We report a simple and reliable method of resolving fringe ambiguities of a wide-field Michelson interferometer by measuring the interference visibility of a noncollimated single-frequency laser beam. Theoretical analysis shows that the interference visibility is sensitive to a subfringe phase shift, and a wide range of beam arrangements is suitable for real implementation. In an experimental demonstration, a Michelson interferometer has an optical path difference of $7\mathrm{mm}$ and a converging monitoring beam has a numerical aperture of 0.045 with an incidental angle of $17°$ . The resolution of visibility measurements corresponds to $\sim 1/16$ fringe in the interferometer phase shift. The fringe ambiguity-free region is extended over a range of $\sim 100$ fringes.