RMagick LoadError

I installed RMagick 2.9.1 and tried to test RMagick code below. irb -rubygems -r RMagick But I got an error like below.

/usr/local/lib/ruby/gems/1.8/gems/rmagick-2.9.1/lib/RMagick2.so: libMagickCore.so.2: cannot open shared object file: No such file or directory - /usr/local/lib/ruby/gems/1.8/gems/rmagick-2.9.1/lib/RMagick2.so (LoadError)         from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `require'         from /usr/local/lib/ruby/gems/1.8/gems/rmagick-2.9.1/lib/RMagick.rb:11         from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `gem_original_require'         from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in `require'         from /usr/local/lib/ruby/1.8/irb/init.rb:252:in `load_modules'         from /usr/local/lib/ruby/1.8/irb/init.rb:250:in `each'         from /usr/local/lib/ruby/1.8/irb/init.rb:250:in `load_modules'         from /usr/local/lib/ruby/1.8/irb/init.rb:21:in `setup'         from /usr/local/lib/ruby/1.8/irb.rb:54:in `start'         from /usr/local/bin/irb:13

I searched and referred http://rmagick.rubyforge.org/install-faq.html#loaderror So I inserted code below to ".bash_profile" export LD_LIBRARY_PATH=/usr/local/lib

But still same error occur ande doesn't work. Any advise?