A MEMS device includes a substrate, a MEMS element portion disposed on a surface of the substrate, a cap having a cavity formed to oppose the MEMS element portion, and a diffusion prevention layer formed on at least a portion of the cap, wherein at least one of the cap and the substrate includes a bonding layer disposed outside of the cavity, and wherein the cap includes a spreading prevention portion disposed between the bonding layer and the cavity and having a V-shape in cross-section.