This insulating structure is for a fuel cell stack or a fuel cell of the fuel cell stack. The fuel cell stack includes a membrane electrode assembly with a peripheral frame and a pair of separators that hold the frame and the membrane electrode assembly in between and is formed by stacking a plurality of sets of the membrane electrode assembly and the pair of separators. The insulating structure includes: a coupling member disposed on at least a part of an outer periphery of the fuel cell stack or the fuel cell; and a projection formed on the coupling member in an area surrounded by the pair of separators and the frame.