How to resolve "cannot load such file -- iconv" in Rhodes framework

Question

I would like to create a new app using the Rhodes framework but I have some errors like this:

C:\Users\TOUCH>rhodes app pharma
C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:120:in `require': cannot load such file -- iconv (LoadError)
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:120:in `require'
        from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/activesupport-2.3.18/lib/active_support/inflector.rb:3:in `<top (required)>'
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:68:in `require'
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:68:in `require'
        from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/activesupport-2.3.18/lib/active_support/core_ext/integer/inflections.rb:1:in `<top (required)>'
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:68:in `require'
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:68:in `require'
        from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/activesupport-2.3.18/lib/active_support/core_ext/integer.rb:2:in `<top (required)>'
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:68:in `require'
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:68:in `require'
        from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/activesupport-2.3.18/lib/active_support/core_ext.rb:8:in `block in <top (required)>'
        from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/activesupport-2.3.18/lib/active_support/core_ext.rb:8:in `each'
        from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/activesupport-2.3.18/lib/active_support/core_ext.rb:8:in `<top (required)>'
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:68:in `require'
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:68:in `require'
        from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/activesupport-2.3.18/lib/active_support.rb:56:in `<top (required)>'
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:68:in `require'
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:68:in `require'
        from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/rhodes-3.5.1.12/res/generators/rhogen.rb:6:in `<top (required)>'
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:120:in `require'
        from C:/Ruby22-x64/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:120:in `require'
        from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/rhodes-3.5.1.12/bin/rhogen:5    :in `<top (required)>'
        from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/rhodes-3.5.1.12/bin/rhodes:4    :in `load'
        from C:/Ruby22-x64/lib/ruby/gems/2.2.0/gems/rhodes-3.5.1.12/bin/rhodes:4    :in `<top (required)>'
        from C:/Ruby22-x64/bin/rhodes:22:in `load'
        from C:/Ruby22-x64/bin/rhodes:22:in `<main>'

How can I resolve it?