This paper proposes a novel integrated multistage energy harvester to scavenge the mechanical energy from human footstep during walking. The device involves a four-stage force amplification using wedge mechanism, leverage mechanism, half-bridge mechanism, and bridge-type force amplifier. It is devised to magnify the input force exerted on a piezoelectric stack so as to enhance the power output. By fully exploiting the characteristics of the force amplification frame, the harvester also provides the function of position protection, which enables the bearing of large load and thereby protecting the piezoelectric stack. By this, the maximum displacement input is restricted to a certain range to ensure the walking comfort. A static analytical model of the energy harvester is established through the force analysis based on the stiffness matrix method. The main architectural parameters of the device are optimized by adopting a multiobjective genetic algorithm with ANSYS software. Moreover, a prototype is fabricated for experimental investigation. Experimental results show that the harvester exhibits a large force amplification ratio of 17.9 and high-peak power output of 50.8 mW across a matched resistor.