A novel circuit topology of the Z-source dc/dc converter, 'Common grounded Z-source buck-boost converter' is proposed. The proposed converter realizes the buck gain in addition to the boost gain in the positive output voltage range, which was only realized in the negative output voltage range in the previous research. Furthermore, the proposed topology provides a common ground for the input voltage source and for the load resistance even though a Z-source network is installed. The theoretical approach for the circuit operation, the simulation results, and the experimental results are introduced.