Circular cylinders in various arrangements cause the wake galloping phenomenon during aerodynamic instability. In this paper, a wake-galloping-based electromagnetic energy harvester is proposed and investigated. A front cylinder is fixed, and a downstream cylinder is connected to the cantilever beam in order to increase the amplitude of the system. To conduct the performance evaluation of the system, wind tunnel tests are carried out considering the design parameters, i.e., the gap between the two cylinder and wind speed. The test results verified the performance of the energy harvester system.