Abstract: To set an optimum offset voltage and detect an NRZ signal with a very small amplitude. An NRZ signal amplifying device 2 includes: input-side voltage detection means 13 for detecting a high-level voltage and a low-level voltage of an input signal to the main amplifier 12; output-side voltage detection means 14 for detecting the two signals inverted relative to each other; and offset voltage control means 15 for calculating a center voltage between the detected high-level voltage and low-level voltage, setting an offset voltage at which the center voltage is the center of an appropriate input range of the main amplifier 12 to the offset circuit 11, and finely adjusting the offset voltage, such that a voltage difference between the detected two signals inverted relative to each other and a polarity change point is close to 0.

Abstract: To set an optimum offset voltage and detect an NRZ signal with a very small amplitude. An NRZ signal amplifying device 2 includes: input-side voltage detection means 13 for detecting a high-level voltage and a low-level voltage of an input signal to the main amplifier 12; output-side voltage detection means 14 for detecting the two signals inverted relative to each other; and offset voltage control means 15 for calculating a center voltage between the detected high-level voltage and low-level voltage, setting an offset voltage at which the center voltage is the center of an appropriate input range of the main amplifier 12 to the offset circuit 11, and finely adjusting the offset voltage, such that a voltage difference between the detected two signals inverted relative to each other and a polarity change point is close to 0.