A casing adapted for packing an electronic device is provided. The casing includes a shell, a cover, and a thermal switch. The shell has an assembly opening, and the cover is adapted for being installed to the assembly opening. The shell and the cover surround the electronic device. The thermal switch is disposed in one of the shell and the cover. When the thermal switch is heated by the electronic device and the temperature thereof rises, the deformation of the thermal switch forms the interference between the cover and the shell so as to prevent the cover being departed from the shell. Therefore, the present invention is capable of avoiding the user from being scalded by the electronic device.