PURPOSE: To obtain a correct waveform of an R wave by arranging an R wave detection circuit to control to turn OFF an analog switch circuit inside synchronizing a pacemaker pulse suppression signal generated with a pacemaker pulse detection circuit.

CONSTITUTION: An absolute value conversion circuit 1 cuts undesired low-pass frequency components and a negative signal inputted is converted to a positive signal to be inputted into an addition circuit 2. A band pass filter 3 selects a frequency component of a pacemaker pulse to be converted to a positive component with a positive polarity conversion circuit 4. A comparator one-shot circuit 5 detects a pacemaker pulse alone exceeding a fixed level predetermined. An R wave detection circuit 7 performs an OFF control of an analog switch inside only while the pacemaker pulse exists by a pacemaker pulse suppression signal eR varying positive and negative from the one-shot circuit 5. Thus, the pacemaker pulse being inputted together with an R wave is cut from a synthetic input signal E1 inputted and an R wave detection signal eOR is outputted.