In recent years, computer simulations have become indispensable in materials research. In particular, they are expected to play a key role in the development of new materials, as well as in the investigation of the mechanisms underlying their properties. Also, they are expected to have high accuracy, large-scale capability, high-speed calculations and a wide range of analysis functions. We have developed a first-principles electronic structure calculation program PHASE/0, based on density functional theory to meet these requirements. Equipped with a variety of analytical functions, it enables direct comparison with experiments. It also provides a range of tools for analysis and visualization, as well as a graphical user interface (GUI) that simplifies them. We have made this program publicly available and apply it to research on materials such as low-dimensional systems, battery materials.