Japan Atomic Energy Research Institute (JAERI) has been conducting R&D on thermochemical hydrogen production using the water-splitting iodine–sulfur process, as part of the research programs striving to utilize heat from a high temperature gas-cooled reactor (HTGR). The R&D is currently at the bench-scale stage and covers several fields including the evaluation of structural materials in corrosion environments, the improvement in thermal efficiency and the techniques for an operation in a closed-loop continuous hydrogen production. Preliminary experimental examinations were carried out to investigate compositions of the solutions for the Bunsen reaction, on which the operation is based. An experimental facility made of glass and fluorine resin for a closed-loop continuous hydrogen production has been operated. In the experiment, hydrogen production at the rate of 32l/h for 20h was successfully accomplished. Feasibility of the operating stability was almost demonstrated. Hereafter, automation of the operation to maintain the process in a stable state is one of the challenges.