NIMS-OS (NIMS Orchestration System) is an open-source software that aims to easily create a closed loop in autonomous automated materials exploration without human intervention. Three main programs are implemented in the Python language and are performed sequentially in the NIMS-OS. The three programs are: AI program that suggests candidate materials to be tested in robotic experiments, a program that creates an input file for the robotic experiments and starts the experiments, and a program that analyzes the experimental results and updates the candidate materials database file. Currently, the Bayesian optimization method (PHYSBO), the boundless objective-free exploration method (BLOX), and the active learning method for phase diagrams (PDC) are implemented as AI program. A GUI version has also been developed so that anyone can easily perform autonomous automated experiments.