A method is provided in which Form-I crystal of 2-{4-[N-(5,6-diphenylpyrazin-2-yl)-N-isopropylamino]butyloxy}-N-(methylsulfonyl)acetamide is administered as an active ingredient to a subject for the purpose of treating or preventing certain diseases, disorders, and symptoms, or for promoting angiogenesis or gene therapy. The Form-I crystal exhibits diffraction peaks in its X-ray powder diffraction spectrum at least at the following angles of diffraction 2θ when the spectrum is obtained by using Cu Kα radiation: 9.4 degrees, 9.8 degrees, 17.2 degrees, and 19.4 degrees. The targeted diseases and disorders include transient ischemic attack, diabetic neuropathy, diabetic gangrene, peripheral circulatory disturbance, connective tissue disease, reocclusion/restenosis after percutaneous transluminal coronary angioplasty, arteriosclerosis, thrombosis, hypertension, pulmonary hypertension, ischemic disorder, angina, glomerulonephritis, diabetic nephropathy, chronic renal failure, allergy, bronchial asthma, ulcer, pressure ulcer (bedsore), restenosis after coronary intervention, thrombocytopenia by dialysis, the diseases in which fibrosis of organs or tissues is involved, erectile dysfunction, inflammatory bowel disease, and gastritis.