A fuel cell device is disclosed that is capable of being made compact when being transported and in storage. The fuel cell device includes a fuel cell unit including a number of fuel cells arranged sequentially in a case. The case includes a holder frame for holding the fuel cells, a first hemi-case, and a second hemi-case. The width of the case is adjustable in the direction in which the fuel cells are arranged in a line. When the fuel cell device is being transported or in storage, the first hemi-case and the second hemi-case are pushed to approach each other, making the size of the case small. When the fuel cell device is used to generate electrical power, the first hemi-case and the second hemi-case are pulled apart from each other and, accordingly, the fuel cells are separated from each other by a springy plate.