An amplitude determining part (14) USES the voltage (V0-V2), which is detected by a voltage detecting part (13), to determine whether the detection range of the MR element (111) is exceeded.
在振幅判断部(14)中，使用由电压检测部(13)检测出的电压(V 0 - V 2)来判断是否在MR元件(111)的检测范围外。