To accurately position a detecting surface.

In a state in which a sensor body 20 is stored in a case 10, a front detecting surface 20S of the sensor body 20 is exposed to an opening part of the case 10. Plastic spacers 25A and 25B which are plastically deformable and regulates the space between the outer surface of the sensor body 20 and the inner surface of the case 10 by abutting on the deep end surface of the case 10, are formed on the back surface of the sensor body 20. The position and attitude of the sensor body 20 in the case 10 are adjusted by plastically deforming the plastic spacers 25A and 25B so as to crush them, the detecting surface 20S is accurately positioned even if the dimensional accuracy of the sensor body 20 or the case 10 is low.