PURPOSE: To regenerate a signal without needing feedback by providing a level shifter, a buffer circuit and an amplifier whose output is fed back through the switch of the level shifter and a buffer circuit on this amplifier.

CONSTITUTION: The amplifier is provided with a level shifter 1 composed of a capacitor 11 and a switching level shifter 12, the buffer circuit 2 composed of the plural stages of transistors(TRs) 20, 21, and an operational amplifier 15 whose output is fed back via the switch 12 of the level shifter 1 and the TRs 20, 21. In this case, an input is given to the level shifter 1, the output of the level shifter 1 is given to the buffer circuit 2 whose amplification factor is the same, the output of the circuit 2 is given to the inverting terminal of the amplifier 3 and a reference potential is given to the noninverting terminal of the amplifier 3. Furthermore, the output of the amplifier 3 is in feedback connection to the switch 12 of the level shifter 1. Thus, a reproduction output is obtained simply as a reproduction output from the buffer circuit 2 at the input of a signal and no feedback is required at this time.