createinstallmedia: command not found

My OS now is Sierra, I want to create a bootable installer for "EI Captian".

I use the command below, and it turns out "sudo: /Applications/Install OS X EICaptian.app/Contents/Resources/createinstallmedia: command not found".

sudo /Applications/Install\ OS\ X\ EI\Captian.app/Contents/Resources/createinstallmedia --volume /Volumes/Captian --applicationpath /Applications/Install\ OS\ X\ EI\Captian.app --nointeraction

The same happened when I intend to create a bootable installer for "Sierra". (Once I thought it may not be allowed to create a lower version OS installer on a higher OS ?! )

So, how can I solve it?! I want to create a bootable installer on my "Sierra".