He paid £1,400 for the rare book. But he's a secret bidder so no one knows who he is.
Unusual
The man's going to give the book to his 15-year-old daughter as a present once she finishes her exams later this year. Apparently she's a keen collector of rare Potter stuff.
The Potter book went up for auction in Edinburgh - the very city where JK Rowling wrote the book.
The novel is one of the first 500 copies originally printed back in 1997. It's unusual because it has the name Joanne Rowling on the front, instead of JK Rowling which the Potter author's now known as.
Experts thought it would make about £400 - but it made more than three times that.
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