Human motion is a rich source of energy. However, the ultra-low frequency and the irregular feature of the motion make the above prospects still far from being effective. In this work, we present a translation-to-rotation converter for energy harvesting during human walking. We here propose the harvester that enables conversion of low-frequency translational vibration to high-speed rotations and further generates electricity via the electromagnetic effect. The transducer is composed of an internal thread sleeve, an external thread driving shaft, a spring, a gearbox, and a limit frame. Our design features low cost, low fabrication difficulty, and high power density. Experiments conducted under pseudo-walking conditions confirmed that the stiffness of the spring and the pitch of the sleeve are the two key parameters for the performance of the harvester. The harvester mounts in a shoe heel and engages power generation in the whole gait cycle. Test subjects walking with one device with optimal spring stiffness on each shoe produce a peak power of 3.7 watts at a pace frequency of 1 Hz, which is about one magnitude higher than that of shoe-mounted devices under pseudo-walking excitation. Moreover, the proposed device could open an alternative pathway for powering smart wearable or portable electronics.