Talk about a weapon of mass value — Darth Vader’s iconic lightsaber is about to hit the auction block … and this bad boy’s expected to rake in Jedi-mind-blowing cash.

TMZ got Brandon Alinger, COO of Prop Store, on cam — and he makes it clear, this isn’t some random hunk of plastic … it’s the screen-matched Hero Dueling Lightsaber used by Vader in “The Empire Strikes Back” and “Return of the Jedi.”

Catch the full clip … ’cause Brandon gives us his prediction of what he thinks it’ll fetch, and the number is high, especially since the absentee bid is already over a million bucks!

The 3-day auction runs September 4 through 6 … and it’s basically nerd heaven. Other goodies up for sale include Tobey Maguire’s “Spider-Man 2” costume, Michael Keaton’s “Batman” ’89 Batsuit & more.