To accurately associate a component with small error of a size due to a vibration, impact or the like by facilitating altering work of an operation of a signal converter.

A core 30 is disposed through an explosion-proof case 15. And, an exciting coil 8 is mounted at a horizontal core part 30a disposed in the case 15. A flapper is formed of two magnetic iron pieces 35, 36 opposed via space forming members 31, 32, and oscillatorily supported by a fulcrum spring 37. The flapper and the spring 37 constitute a seesaw structure 55. And, the structure 55, a permanent magnet 9, the members 31, 32 and a yoke 40 are unitized by molding resin 39 to a magnet unit 57. The unit 57 is mounted so as to be front-to-rear invertible at vertical core parts 30b, 30c out of the case of the core 30.