TOKYO, Jan 17 (Reuters) - The Nikkei stock average dropped on Friday as disappointing U.S. corporate earnings hurt sentiment, but the market pared its losses on optimism over Japan's third-quarter reporting season due to kick off later this month. Mitsubishi Motors Corp outperformed the market, ending 10 percent higher as some short-term investors cut their short positions in the Japanese automaker that they had been building up ahead of a public share offering. The Nikkei average ended 0.1 percent lower at 15,734.46, after earlier falling as much as 0.8 percent. For the week, the index dropped 1.1 percent. The broader Topix gained 0.2 percent to 1,297.39. The JPX-Nikkei Index 400, a recently introduced gauge comprised of firms with high return on equity and strong corporate governance, edged up 0.2 percent to 11,712.09. In afternoon trade, Nippon Steel & Sumitomo Metal Corp's widened its losses after a fire erupted at its steel plant in central Japan. The stock ended 1.5 percent lower.