"Pawn Stars" star Corey Harrison is thrilled his father, Rick, is getting married -- and he's more than happy to be his best man ... if that's what Rick decides.

Corey tells TMZ ... this will be the third time he's attending one of Rick's weddings -- having been by his dad's side when he got hitched to Tracy Harrison in 1986 and Deanna Burditt in 2013.

"Big Hoss" says he'd be honored to be his dad's best man, but Rick shouldn't expect a bachelor party or a gift. Corey doesn’t think his dad would want a bachelor party, and jokes, "You can't keep getting married every time you need a toaster!"

As we reported, on a visit to Chile, Rick popped the question to his girlfriend, Angie Polushkin -- a Vegas nurse 18 years younger than him -- presenting her with a ring he considers one of his most prized possessions from his iconic Gold & Silver Pawn Shop in Las Vegas.

Corey approves of Rick's fiancée ... telling us he's met Angie several times and thinks she's great, and most importantly, she clearly loves Rick. He quips that she's a perfect fit for the family ... she must be a little "screwed up" if she likes Rick!

Corey's hoping Rick and Angie go the distance ... mainly so he doesn't have to take care of his dad when he's older!