A connecting device includes: a shaft; a drum that has a container defined therein and is rotatably disposed on the shaft; a stator that is fixed to the shaft and is contained inside of the container; a rotator that is fixed to the drum, is rotatably disposed on the shaft, and is contained inside of the container with an interval with respect to the stator; first terminals that are disposed in the stator; second terminals that are disposed in the rotator and are brought into contact with the first terminals, respectively; a connecting cord that is wound around the drum, and has a connecting plug to be connected to a vehicle at one end thereof whereas is electrically connected to the second terminals at the other end thereof; a power supply cord having a power source plug electrically connected to the first terminals at one end thereof whereas connected to an outside power supply at the other end thereof; and a leakage detector contained inside of the container.