Abstract: An apparatus for measuring potential variations in the human body, comprising: a pair of conductors, an attachment patch for attaching the conductors to the measurement sites; an amplifier that amplifies, as AC signals, the potential variations input from the conductors through connecting wires, a transmitter that transmits the amplified signals, a battery that supplies electric power to the amplifier and transmitter, a voltage-divider circuit that divides the voltage applied from the battery, and a compensator circuit that applies a voltage so divided to the amplifier as a reference voltage and, concurrently, rejects DC components input to the conductors, using the divided voltage as a reference voltage. Hence is provided a compact apparatus for measuring body signals such as myoelectric potentials, without restricting the movements of the test subject.