A conductor rail comprising a main body having a facing cap mounted thereon. The second insulating film is formed to fill the concave portions and a portion between the first and second gate electrodes has a multi-layered structure containing at least the first and second insulating films. In order to correctly detect the damages based on the pressure difference, an exhaust gas volume flowing through the collector is increased to a target volume by raising exhaust gas temperature. The first rack segment is flexibly deformable so as to overcome a conflict of alignment of gear teeth of the gear and the first rack segment when such conflict occurs.