As of 9:15 a.m., the 225-issue Nikkei Stock Average lost 78.82 points, or 0.35 percent, from Friday to 22,399.97.
The broader Topix index of all First Section issues on the Tokyo Stock Exchange, meanwhile, dropped 4.31 points, or 0.27 percent, at 1,578.49.
Mining, land transportation and construction-linked issues comprised those that declined the most in the opening minutes after the morning bell.
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