In a brake disc rotor 1, at least a road wheel mounting plane 6 is covered with a rust preventive coating 8 of rust preventive paint. A protection determination section determines whether or not the content data needs to be protected according to the protection information. An indicator coupled to the exhaust tube indicates when fluid is exiting the exhaust tube. The slope compensation circuit comprises an output configured to provide a slope compensation signal. The first lumen communicates with the space inside the expandable body and the expandable body expands by the internal pressure of the fluid which is injected from the opening at one end and enters the space inside the expandable body through the first lumen.