PURPOSE: To enable execution of detection of very high precision by providing a superposing circuit which superposes outputs of two sensors of a low frequency type and a high frequency type and delivers the same.

CONSTITUTION: A low-frequency type sensor 1, a high-frequency type sensor 3, amplifiers 3 and 4 and a superposing circuit 5 are provided, and outputs of the sensors 1 and 2 are amplified respectively by the amplifiers 3 and 4 and inputted to the circuit 5. A required frequency (f) in a band wherein the gains of the sensors 1 and 2 do not attenuate is taken as the boundary, and the output S of the sensors 1 and 2 are superposed and delivered. The circuit 5 has two functions of a low-pass filter passing a frequency band lower than the frequency (f) and a high-pass filter passing a frequency band higher than that, in a system wherein a low-frequency detection signal Q1 from the sensor 1 and a high-frequency detection signal Q2 from the sensor 2 are coupled in diodes 5c and 5d by using operational amplifiers 5a and 5b. Since the outputs of the two sensors can be taken out continuously in an integral and inseparable manner, responsiveness in a large band width from a direct-current component to a high-frequency component is exhibited and detection of very high precision can be executed.