How can I install Startup Disk Creator on Ubuntu 17.04?

If you cannot find it just install it running in terminal those commands (first two are optional, to update the repos, and upgrade what should be upgraded, but if you just want to make pendrive with installer, just skip to the third line.

sudo apt update
sudo apt upgrade
sudo apt install usb-creator-gtk

For me it worked, Ubuntu tutorials and forums stated that it is build in, from 18.04, but it's not if you have other flavor than "vanilla" Ubuntu, for example Budgie.

Then you may also start this from terminal:

usb-creator-gtk