gvim on windows does not accept Alt modifier key

hello, everyone

when i press Alt-<printable character>, it seems that gvim only takes
<printable character>; it cannot detect that Alt is pressed

trying winaltkeys seems not working:
set winaltkeys=no

mapping itself seems working:
noremap <M-N> :echo "M-n works!"<CR>
map <C-N> <M-N>

this yields :map
<C-N> <M-N>
<M-N> * :echo "M-n works!"<CR>
and Ctrl-N prints "M-n works!", while Alt-N is taken regarded as N
resulting in searching functionality

does anyone have idea that force gvim to interpret Alt modifier key?

i'm using japanese patched gvim on windows 7 64bit, which is distributed
by http://www.kaoriya.net/software/vim

thanks

--
output of :version

VIM - Vi IMproved 7.3 (2010 Aug 15, compiled Feb 14 2013 09:47:55)
MS-Windows 64 ビット GUI 版
適用済パッチ: 1-816
Modified by koron.kaoriya@gmail.com
Compiled by koron.kaoriya@gmail.com
Big 版 with GUI. 機能の一覧 有効(+)/無効(-)
+arabic +autocmd +balloon_eval +browse ++builtin_terms +byte_offset
+cindent +clientserver +clipboard +cmdline_compl +cmdline_hist
+cmdline_info +comments +conceal +cryptv
+cscope +cursorbind +cursorshape +dialog_con_gui +diff +digraphs -dnd
-ebcdic +emacs_tags +eval +ex_extra +extra_search +farsi +file_in_path
+find_in_path +float +folding -footer
+gettext/dyn +guess_encode -hangul_input +iconv/dyn +insert_expand
+jumplist +keymap +kaoriya +langmap +libcall +linebreak +lispindent
+listcmds +localmap +lua/dyn +menu
+migemo/dyn +mksession +modify_fname +mouse +mouseshape
+multi_byte_ime/dyn +multi_lang -mzscheme +netbeans_intg -ole
+path_extra +perl/dyn +persistent_undo -postscript +printer
-profile +python/dyn +python3/dyn +quickfix +reltime +rightleft
+ruby/dyn +scrollbind +signs +smartindent -sniff +startuptime
+statusline -sun_workshop +syntax +tag_binary
+tag_old_static -tag_any_white -tcl -tgetent -termresponse +textobjects
+title +toolbar +user_commands +vertsplit +virtualedit +visual
+visualextra +viminfo +vreplace +wildignore
+wildmenu +windows +writebackup -xfontset -xim -xterm_save +xpm_w32
システム vimrc: "$VIM\vimrc"
ユーザ vimrc: "$HOME\_vimrc"
第2ユーザ vimrc: "$VIM\_vimrc"
ユーザ exrc: "$HOME\_exrc"
第2ユーザ exrc: "$VIM\_exrc"
システム gvimrc: "$VIM\gvimrc"
ユーザ gvimrc: "$HOME\_gvimrc"
第2ユーザ gvimrc: "$VIM\_gvimrc"
システムメニュー: "$VIMRUNTIME\menu.vim"
コンパイル: cl -c /W3 /nologo -I. -Iproto -DHAVE_PATHDEF -DWIN32
-DFEAT_CSCOPE -DFEAT_NETBEANS_INTG -DFEAT_XPM_W32
/DMODIFIED_BY=\"koron.kaoriya@gmail.com\"
/DDYNAMIC_MSVCRT_DLL=\"msvcr100.dll\" /DGETTEXT_DLL=\"intl.dll\"
/D_BIND_TO_CURRENT_VCLIBS_VERSION=1 -DWINVER=0x0400
-D_WIN32_WINNT=0x0400 /Fo.\ObjGULYHRAMD64/ /Ox /GL -DNDEBUG /MD
-DFEAT_MBYTE_IME -DDYNAMIC_IME -DFEAT_GUI_W32 -DDYNAMIC_ICONV
-DDYNAMIC_GETTEXT -DDYNAMIC_MIGEMO -DFEAT_LUA -DDYNAMIC_LUA
-DDYNAMIC_LUA_DLL=\"lua52.dll\" -DFEAT_PYTHON -DDYNAMIC_PYTHON
-DDYNAMIC_PYTHON_DLL=\"python27.dll\" -DFEAT_PYTHON3 -DDYNAMIC_PYTHON3
-DDYNAMIC_PYTHON3_DLL=\"python33.dll\" -DFEAT_PERL -DDYNAMIC_PERL
-DDYNAMIC_PERL_DLL=\"perl516.dll\" -DFEAT_RUBY -DDYNAMIC_RUBY
-DDYNAMIC_RUBY_VER=19 -DDYNAMIC_RUBY_DLL=\"msvcr80-ruby191.dll\"
-DFEAT_BIG /Fd.\ObjGULYHRAMD64/ /Zi
リンク: link /RELEASE /nologo /subsystem:windows /LTCG:STATUS
oldnames.lib kernel32.lib advapi32.lib shell32.lib gdi32.lib
comdlg32.lib ole32.lib uuid.lib /machine:AMD64 /nodefaultlib gdi32.lib
version.lib winspool.lib comctl32.lib advapi32.lib shell32.lib
/machine:AMD64 /nodefaultlib msvcrt.lib user32.lib
/nodefaultlib:lua52.lib /nodefaultlib:python27.lib
/nodefaultlib:python33.lib WSock32.lib
..\..\contrib\xpm\x64\lib\libXpm.lib /PDB:gvim.pdb -debug

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