The invention provides a sensor that is attached to a sensor fixing portion by a threaded joint method through using a threaded joint clamping portion, and that can specify a rotational direction position of the sensor with respect to the sensor fixing portion. The sensor has a sensor body portion, a flange portion, a threaded joint clamping portion, and a buffer portion. The buffer portion has arotation stop portion and a welding fixing portion. The front end surface and the outer peripheral surface of the outer surface of the buffer portion have heat burning regions, and the rear end surface of the outer surface of the buffer portion just has a common region but has no a heat burning region. Since the rear end surface of the buffer portion has no heat burning region, frictional force between the rear end surface of the buffer portion and the threaded joint clamping portion can be suppressed from increasing, and damages of the rotation stop portion of the buffer portion caused by frictional force of the threaded joint operation by the threaded joint clamping portion. Therefore, rotation of the buffer portion in threaded joint operation by the threaded joint clamping portion can be suppressed, and rotation of the sensor can also be suppressed. Thus, the sensor can be prevented from being displaced.