As miniaturized imaging devices are used more frequently for biomedical purposes such as diagnoses or surgeries, the demands for smaller, thinner lenses increases. In conventional macroscopic lenses, more aberration occurs as the thickness is reduced. Metalenses overcome this limitation by controlling the phase of light with subwavelength-scale nanostructures. However, conventional metalenses are designed to focus light in a single or narrow wavelength range, and cannot concentrate light on focus that deviates from the target wavelength due to severe aberration. We proposed an ultrathin silicon nitride metalens that operates in the full range of visible light. Silicon nitride metalens was designed to have a total diameter of 60$\mu m$ and a focal length of 250$\mu m$ at 633nm wavelength. The metalens concentrated light at distances of 250$\mu m$ and 320$\mu m$ from the lens for 633nm and 533nm lasers, respectively, and obtained images of the object in the entire wavelengths of light. The proposed silicon nitride metalens will present new approaches for ultrathin imaging devices.