While I was in problem in installing node.js in Ubuntu. I found above article.
Key point is "
DO NOT RUN sudo apt-get install node
"node is not node.js. node (in ubuntu) is different packages..
Thanks guys.
---V2
Above document is right and wrong.
I found below in nodejs.org . It works.
sudo apt-get install python-software-properties
sudo add-apt-repository ppa:chris-lea/node.js
sudo apt-get update
sudo apt-get install nodejs npm
-- Finally Not worked... The problem is the version dependency 
