A device and method for detecting biological information without being affected by sudden-onset signal even when sudden-onset large vibration is caused while driving a vehicle or the like. Peak input and output values of a variable delay device are detected, and the difference between the values is determined by a subtractor. The difference is compared to a predetermined threshold to obtain a positive or negative output as an up/down selection output for an up/down counter. The output of the up/down counter is sent to a variable delay device with a clock generated based on an inputted peak signal of biological information to obtain a variable delay amount corresponding to one cycle of the biological information. When the subtractor output exceeds the predetermined threshold, a predetermined output voltage is generated, and an amplifier connected to the variable delay device is controlled so that the gain of the amplifier becomes zero.
