TOKYO (Dow Jones)--Japanese core machinery orders fell a surprisingly steep 15.6% in January from a month earlier, the government said Monday, suggesting private investment will remain weak in months ahead. The fall, the second in succession, was much sharper than that expected by economists surveyed by Dow Jones Newswires, who estimated on average that core orders had fallen 4.2%. Machinery orders are widely regarded as a leading indicator of corporate capital investment. Core orders exclude those from electric power companies and those for ships, which are often a source of volatility in the overall data due to their large size. Unadjusted core orders fell 22.2% from the year-earlier month.