From this page:
Make sure to run
sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list'
and
sudo apt-key adv --keyserver hkp://ha.pool.sks-keyservers.net:80 --recv-key 421C365BD9FF1F717815A3895523BAEEB01FA116
and
sudo apt-get update
before running the installation command.
EDIT:
Now that we know that you are on Ubuntu 10.04, we can help you further. Ubuntu 10.04 are officially supported by ROS electric, which you can check out here. Of course, electric is long gone, so a better solution would be to install ROS kinetic from source, but be prepared to have (lots of?) dependency issues since you are using an outdated OS. I would strongly suggest to upgrade your OS if that's possible though.