Ruby – Error installing rmagick: ERROR: Failed to build gem native extension

I am trying to install RmMagic using the below command:

gem install rmagick -v=2.12.2

After running this command i get some error :

Temporarily enhancing PATH to include DevKit...
Building native extensions.  This could take a while...
ERROR:  Error installing rmagick:
        ERROR: Failed to build gem native extension.


        D:/ruby/bin/ruby.exe extconf.rb
checking for Ruby version >= 1.8.5... yes
Invalid drive specification.
Unable to get ImageMagick version
*** 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=D:/ruby/bin/ruby


Gem files will remain installed in D:/ruby/lib/ruby/gems/1.8/gems/rmagick-2
.12.2 for inspection.
Results logged to D:/ruby/lib/ruby/gems/1.8/gems/rmagick-2.12.2/ext/RMagick
/gem_make.out

Please help me in this regard. Thanks in advance.