Abstract: An experimental nuclear fusion reactor comprising a coaxial plasma gun which has an outer electrode and an inner electrode arranged coaxially with each other, a metallic container which generates an annular plasma round a center conductor and which holds a poroidal magnetic flux, an inlet which introduces a plasma from the coaxial plasma gun into the container, and conductor members which electrically connect the center conductor, either of the outer and inner electrodes, the inlet and the container in succession so as to form a closed circuit, wherein current to flow through the closed circuit is controlled to hold a toroidal magnetic flux of the annular plasma.