This paper introduces the current development of autonomous ships in Japan and the guidelines for autonomous ships established by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT); and it considers the liability of the owners of remotely controlled vessels and the phase II-type autonomous ships assumed by the Guidelines in case of a collision at sea. First, it presents the experiments and development of autonomous ships in Japan, where shipping companies, rather than shipbuilding or engineering companies, have led the development of autonomous ships. For example, Nihon Yusen Kaisha (NYK) Group and many other companies spearheaded an autonomous vessel demonstration project called Designing the Future of Full Autonomous Ship (DFFAS). In this project, a conventional container vessel was equipped with autonomous navigation functions and allowed to navigate autonomously from the Port of Tokyo to the Port of Tsu-Matsusaka. Second, in connection with the development of autonomous vessels, the MLIT has recently established two types of guidelines; the “Safety Guideline for Remotely Controlled Small Vessels” in 2019 and “Safety Guideline for Autonomous Vessels” in 2022. This paper introduces the guidelines in Japan to consider legal issues regarding Maritime Autonomous Surface Ships (MASS). Third, this study examines, based on these two guidelines and current laws, what liability would be attached to the owner or manufacturer of a vessel subject to the guidelines in the event of an actual collision.