The "Ghost Adventures" star tells TMZ ... he recently got his hands on the fabled "Exorcism Box," which was used during the 1970s real-life exorcisms of Anneliese Michel ... whose story is the inspiration behind 2005's "The Exorcism of Emily Rose."

Zak tells us he got the box from filmmaker Christopher Saint Booth, who wanted to get rid of it after a disturbing experience, to put it mildly. While he had the box, Booth says he felt something growing inside him, and a doctor determined the growth contained teeth and stem cells.

Booth says he had an archbishop exorcise the box ... and while doing so, he saw a dark figure dart past him. Booth believes it was Anneliese, who died way back in 1976 following 67 catholic exorcism rites.

Zak says Booth told him the archbishop saw the figure too, which appeared to have Anneliese's face, and it was shaking uncontrollably as if being pushed away from the box by a dark energy. Booth believes the "Exorcism Box" absorbed all the energy from Anneliese's exorcisms.

If that doesn't give you enough chills ... Zak also obtained a copy of the infamous Exorcist Diary, which inspired the 1974 movie "The Exorcist."

There are only 6 copies of the diary, 2 of which remain in a vault at the Vatican. The diary documents a 3-month period of exorcisms on a 13-year-old boy in St. Louis way back in 1949 and includes a map of Hell.

Zak says Booth had the diary while working on a documentary called "The Exorcist File" ... and Booth says he felt very oppressed and suicidal whenever the diary was nearby.

And, get this ... Zak says Booth told him he had the diary with him in a hotel room when he saw a horned, shadowy figure appear just before something scratched his ankle and pulled him out of bed. 😱

Since bringing the items to his Haunted Museum in Las Vegas, Zak says countless guests are refusing to enter the new Exorcism Room Exhibit before they even know what's inside ... with some saying they felt light-headed.

Zak is not new to the exorcism world -- he filmed the 100th episode of "Ghost Adventures" in the house where the notorious St. Louis exorcism was performed.

It's a timely acquisition for Zak with Halloween lurking, and "The Exorcist: Believer" just hitting theaters.