In this study, we propose a bistable energy harvester with an auxiliary magnet oscillator (BEH-O), whose motion is mechanically rectified to enhance its broadband energy harvesting performance. The design of the proposed BEH-O system is based on local modification of the double-well potential. The auxiliary oscillator with the mechanical rectifier is designed in such a manner that its rectified half-sine motion tends to reduce the saddle barrier of restoring potential, leading to a possibility of an easier escape from the potential well, while keeping other parts of the potential, thereby maintaining high-energy orbital motion. Consequently, the lower bound of the operating frequency band of the BEH-O is reduced, when compared to its conventional counterpart, i.e., conventional bistable energy harvester (CBEH), while its upper bound remains unchanged. Such a broader frequency band of the BEH-O can be directly compared with that of the CBEH, as there is little difference in the high-energy orbital motion between the two. This beneficial effect of the BEH-O system is theoretically and experimentally supported by bifurcation analyses and frequency response analyses. Published by AIP Publishing.