Lord Justice Leveson is "loading a gun" for the newspaper industry according to Chris Blackhurst, editor of The Independent.
He was reacting to letters sent by the inquiry to give prior notice of possible criticism in the final report.
Mr Blackhurst said he was shocked by the document, which he described as "a damning indictment of my industry".
Lord Justice Leveson said he was disappointed details of the private letters were being "openly discussed".
Hearings for the media ethics inquiry, which was prompted by the News of the World phone-hacking scandal, closed at the end of July, with 650 witnesses testifying in person or in writing.
The correspondence, known as a Rule 13 letter, was sent to all national newspaper groups and major regional companies.
They provide an opportunity for those facing possible criticism to respond in advance of the report's publication.
Chris Blackhurst told BBC Radio 4's The Media Show that he could not discuss the specific contents of the letter for legal reasons but it was "a point by point demolition of the industry".
"The best way I can describe it is he's loading a gun, and this document - well over 100 pages - is all the ammunition. And believe you me there is plenty of ammunition, you read the ammunition and you just gulp."
He said he felt "shock and anger" at how "one-sided" the letter was, calling it "a diatribe" that "throws the book at the industry".
Some of the criticisms in the document were, he said, "certainly justified" but others "raise eyebrows" and did not bear any relation to practices at his paper or other titles at his "end of the market".
"The fact is that newspapers are an adornment to our society. We would be lost without them," he added.
"Story after story, scandal after scandal has been broken by newspapers, not by anybody else. That simply is not reflected in this document."
A spokesman for the inquiry said: "Lord Justice Leveson is disappointed that the contents of confidential letters that he has written are being openly discussed in the press.
"He wants to make it clear that all recipients of these letters - which are issued in accordance with Rule 13 of the Inquiry Rules 2006 - are obliged by this confidence.
"These letters are a standard part of inquiry procedures and give private notice of possible criticism in order that recipients can respond before any concluded view is reached.
"By their nature such letters are, of course, one-sided documents and are not intended (as it makes clear) to deal with the positive aspects of the activities of the press: plainly, no warning is necessary for that purpose."