PURPOSE: To extract signals before and after muting control by forming an output terminal 3 for an amplification output at the output side of an amplifier and providing a buffer circut which performs the muting control over the amplification output.

CONSTITUTION: An input signal to be amplified is supplied from a signal source such as a magnetic head to an input terminal, and an amplifier 4 constitutes a preamplifier which is supplied with the signal directly from the signal source. The output terminal 6 to which an amplification output which is not brought under the muting control is led out is formed on the output side of this amplifier 4, and the buffer circuit 8 which performs the muting control over the amplification output is installed. Consequently, the amplification output V01 of the amplifier 4 is supplied from the output terminal 6 to a signal processing system which does not require the muting control and an amplification output V02 is supplied from the output terminal 12 of the buffer circuit 8 to a signal processing system which requires the muting control through the buffer circuit 8.