Failed to build gem native extension [windows 7][Rubyinstaller 2.2.5]

[NikolayMurha]

Hello. I try to install gem on windows platform but I have error.
I try 64 and 32 bit versions, but I have same result.
Other native extensions installed ok.

C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/sigar-0.7.3/bindings/ruby
C:/Ruby22-x64/bin/ruby.exe -r ./siteconf20161021-8004-1qe27k9.rb extconf.rb
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=C:/Ruby22-x64/bin/$(RUBY_BASE_NAME)
C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:55:in
`require': cannot load such file -- ftools (LoadError)
from
C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:55:in
`require'
        from extconf.rb:39:in `<main>'
Ruby platform=x64-mingw32

extconf failed, exit code 1

Gem files will remain installed in
C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/sigar-0.7.3 for inspection.
Results logged to
C:/Ruby22-x64/lib/ruby/gems/2.2.0/extensions/x64-mingw32/2.2.0/sigar-0.7.3/gem_make.out