A usable 13.5 nm radiation source in which Sn is the radiation substance, in which rapid transport with good reproducibility is possible up to the plasma generation site and in which formation of detrimental "debris" and coagulation of the vapor are suppressed as much as possible is achieved using emission of Sn ions in that SnH₄ is supplied continuously or intermittently to the heating/ excitation part, is subjected to discharge heating and excitation or laser irradiation heating and excitation, and thus, is converted into a plasma from which extreme UV light with a main wavelength of 13.5 nm is emitted.