In Big, what does Josh Baskin use at the fair to wish that he were an adult?

In Big, Josh Baskin uses a Zoltar machine to wish that he were an adult.

After being embarrassed at a fair, Josh finds the coin-operated fortune-telling machine and makes his wish. The next morning, he has become an adult, although he retains his childhood mind. His sudden transformation launches the film’s comedy and its exploration of responsibility, work, friendship, and growing up.

The Zoltar machine is a fictional carnival device created for the story. It is often remembered as a fortune-teller or arcade machine, but Zoltar is the specific name shown in the film. Big was released in 1988, directed by Penny Marshall, and starred Tom Hanks as the adult Josh.