PURPOSE: To reduce low frequency noise without decreasing S/N for high frequency noise by connecting one point of a signal line including a DC-fraction breaking condenser to a voltage source through an active element forming a switch and a high-pass filter.

CONSTITUTION: A capacitor 6 disconnecting a DC-fraction of a signal, a switch 7 clamping a constant voltage for a certain period of a signal, and a buffer circuit 9 receiving the clamped signal are connected to a signal line 21 of a signal which outputs information intermittently. The switch 7 is turned on for some period in an ineffective period of the inputted signal through the capacitor 6, and a signal voltage for this period is made into a constant voltage. Moreover, an active element 22 such as a resistance and an inductance is connected between the signal line 21 and the switch 7, and when the switch 7 is turned on, the active lement 22 becomes a high-pass filter.