The present invention provides for a bolt structure for use with a magnesium alloy member that can insulate between magnesium alloy members and steel or other bolts without lowering the bolt shaft power, and prevent occurrence of electrolytic corrosion with an electrolyte such as water. The NOX sensor section includes a first pumping cell adapted to pump oxygen into or out of a gas under measurement introduced into a first measurement chamber, and a second pumping cell communicating with the first measurement chamber and configured such that a second pumping current Ip2 corresponds to an NOX concentration of the gas under measurement. The first collector layer is made of a doped or undoped semiconductor in such a way as to contact the sub-collector region.