I cannot install pg gem on windows

I am practicing simple blog and when I am using gem install pg on GIT or cmd, I am having this:

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

    d:/Development/RailsInstaller/Ruby2.1.0/bin/ruby.exe extconf.rb
checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
 --with-pg-config=/path/to/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** 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:/Development/RailsInstaller/Ruby2.1.0/bin/ruby
        --with-pg
        --without-pg
        --enable-windows-cross
        --disable-windows-cross
        --with-pg-config
        --without-pg-config
        --with-pg_config
        --without-pg_config
        --with-pg-dir
        --without-pg-dir
        --with-pg-include
        --without-pg-include=${pg-dir}/include
        --with-pg-lib
        --without-pg-lib=${pg-dir}/lib

extconf failed, exit code 1

Gem files will remain installed in d:/Development/RailsInstaller/Ruby2.1.0/lib/r
uby/gems/2.1.0/gems/pg-0.18.1 for inspection.
Results logged to d:/Development/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/ex
tensions/x86-mingw32/2.1.0/pg-0.18.1/gem_make.out