MSDNにちゃんと出てるよ。だいたい32000ってのはUNICODE_STRING の制限と思われ(DDK参照)。 http://msdn.microsoft.com/library/en-us/fileio/filesio_7wmd.asp > Windows NT/2000/XP: In the ANSI version of this function, > the name is limited to MAX_PATH characters. To extend this > limit to nearly 32,000 wide characters, call the Unicode version > of the function and prepend "\\?\" to the path. For more > information, see File Name Conventions.