Idiopathic pulmonary fibrosis(IPF) is chronic progressive fibrosing lung disease of unknown cause. There is no effective therapy yet for this disease and the mean survival in most reports is about 3 years after the diagnosis. Because of the stiff fibrosis of the lung, pulmonary hypertension is the late complication of IPF and its development heralds a very poor outcome of the patients. For the primary pulmonary hypertension, recently the effective drugs have been available. However, there is no study about the efficacy of these drugs in the patients with pulmonary hypertension secondary to pulmnary fibrosis, and the aim of this trial is to study the safty and efficacy of "Iloprost," one of the safe and effective drugs in primary pulmonary hypertension.