This paper presents the design, fabrication and testing of a new piezoelectric energy harvester with a single piezo-stack for harvesting energy from excitations with back and forth motion. A rhombus-type force amplifier is combined with a selectivity lever to utilize both pull and push input. Analytical model is established to predict the force amplification ratio of the proposed energy harvester under different directions of input force. In order to maximize the output performance of the energy harvester, the mechanism parameters are optimally designed. A prototype energy harvester is fabricated for experimental testing. Results indicate that the developed harvester has the merits of high safety factor and compact size, which can be adopted to harvest the mechanical energy for excitations with both pull and push input.