 This local, prospective, non-interventional, multi-center study includes patients treated with Riociguat for PAH. A total of 600 patients valid for safety analysis is planned to be included in 4 years. This study is performed as an all-case investigation therefore; all patients who receive Riociguat treatment for PAH need to be registered, in principle. The treatment should be performed based on the product label in Japan. The standard observation period will last for 12 months from starting Riociguat treatment. Safety and effectiveness will be evaluated at the 3rd and 12th month of treatment. In addition, the extension observation period will be carried out as long as Riociguat treatment continues or at most for more 6 years. The purpose is to collect information on safety and effectiveness, such as adverse events and clinical worsening of PAH, once a year. Combining the standard observation and the extension observation period the patient could be followed for at most 7 years. When Riociguat treatment is terminated, the observation of the patient ends. The investigator should record data for each patient, as defined in the protocol, using the Electronic Data Capture EDC system. The duration of the study is of approximately 8 years from PAH indication approval. 