This paper presents the design, fabrication and testing of a novel piezoelectric energy harvester with a single piezo-stack for harvesting energy from excitations with bidirectional motion. A rhombus-type force amplifier is combined with a selectivity lever to utilize both pull and push inputs. 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 inputs in bidirectional directions.