This disclosure describes a fuel cell device having a unit cell structure including a pair of separators stacked on each side of a membrane electrode assembly via diffusion layers, the pair of separators including a number of grooves and convex parts extending between the grooves formed on a side of a contact surface with the gas diffusion layers, one of the pair of separators being a hydrogen electrode side separator having the grooves as hydrogen channels and the other of the pair of separators being an air electrode side separator having the grooves as air channels. The respective grooves of the air electrode side separator have the same width and are arranged at equal intervals, and the respective grooves of the hydrogen electrode side separator have the same width as that of the respective grooves of the air electrode side separator.