Coupling device and refrigerant circulation device

A coupling device comprising:

• a first connection portion connectable to an external socket or plug, the first connection portion including a first flow path through which a fluid flows;
• a second connection portion including a first inner surface defining a second flow path continuous with the first flow path, and a first outer surface positioned farther outward than the first inner surface;
• a tube portion including an end portion into which the the second connection portion is inserted and a second inner surface positioned outside the first outer surface and defining a third flow path;
• and
• a sealing portion interposed between the first outer surface and the second inner surface;
• wherein
• a thermal expansion coefficient of the sealing portion is smaller than a thermal expansion coefficient of the first outer surface and larger than a thermal expansion coefficient of the second inner surface.