The negative-resistance effect recently predicted for current-controlled highly damped Josephson junctions is experimentally demonstrated at a frequency of 9 GHz. Characteristically, the pump (or Josephson) frequency is smaller than the amplified one, and the pump mechanism is effective over a broad range of frequencies in contrast to the conventional parametric negative-resistance effect where the pump frequency exceeds that of signal and idler and where the frequency of operation is limited to a narrow range. The broad-band feature renders operation uncritical to tuning and bias voltage fluctuations. The fact that the junction is the element of lowest impedance in the circuit alleviates to a degree the matching problem generally encountered with Josephson contacts.