David Irving pleads guilty, says Holocaust views have changed
"I acknowledge my guilt on this charge," Irving said, seated behind a witness stand facing judge Peter Liebetreu.
Irving, who faces a possible 10 years in jail, said he now realised his statement that "there were no gas chambers in Auschwitz (was) false".
But Irving had earlier told reporters upon entering the court in central Vienna in handcuffs that it was "ridiculous for me to be standing here on trial for something I expressed 17 years ago."
"I am not a Holocaust denier," he said. "My views have changed. History is a constantly growing tree... The more documents are available, the more you learn, and I have learned a lot since 1989."
Asked about the Holocaust, he said: "I would call it the Jewish tragedy in World War 2" and that millions of Jews died.
Irving, whose handcuffs were removed as the trial began, insisted on the accuracy of his historical research, as Liebetreu peppered him with questions about Holocaust denials he had made in the past and how he felt about them now.
Irving said he had changed his mind since 1989 after discovering documents, some of them from Adolf Eichmann, who organised the Nazi genocide of the Jews, while on a trip in Argentina.
But Irving insisted on the logic of some of his past statements, such as saying that the fact that 100 000 people survived Auschwitz was a sign that the gas chambers did not exist, even if he now regretted the formulation.
Under questioning from prosecutor Michael Klackl, Irving also refused to say that his statement about the gas chambers was tantamount to denying the Holocaust occurred.
"That was no Holocaust denial, that was only (a statement) about a part of the (Holocaust) history," Irving said.
Klackl later told reporters: "We know about David Irving, that he always tries to arrange every evidence and find many reasons why you should take his argument in the right way."
Klackl said he was "convinced" the jury of six women and two men would reach a verdict Monday, although he refused to speculate on the outcome.
Irving, 67, faces a 10-year prison sentence under an Austrian law that prosecutes those who "deny the genocide by the National Socialists or other National Socialist crimes against humanity."
The right-wing historian was arrested in November after a routine check on a highway in Austria.
The warrant for his arrest was issued by a Vienna court in 1989 after he allegedly denied at meetings in Austria that the Nazi regime used gas chambers in concentration camps.
Irving was on trial for also saying that the November 1938 Kristallnacht pogrom against the Jews was not the work of the Nazis but "unknown" people who had dressed up as storm troopers and that Adolf Hitler had in fact protected the Jews.
The Holocaust was Nazi Germany's systematic slaughter of some six million Jews, mainly in the later years of World War 2.
Irving has become notorious worldwide for attempting to establish, despite overwhelming evidence to the contrary, that Hitler was not party to the Holocaust, that there were no gas chambers in Auschwitz, and that the number of Jews killed by the Nazis was greatly exaggerated.
He has been condemned by the courts several times, notably in Britain and Germany, and last year he was refused entry to New Zealand.
He is reportedly also banned from residing in Australia, Canada, Italy and South Africa as well as Germany.
Irving sparked widespread outrage with his book Hitler's War in 1977, in which he claimed the Nazi dictator did not know about the mass killings of Jews until 1943 and that he never ordered the Holocaust.
In 2000, Irving lost a high-profile libel case in London against US historian Deborah Lipstadt, who called him a "Holocaust denier" in her book, Denying The Holocaust: The Growing Assault On Truth And Memory.
Irving carried a copy of Hitler's War when he entered court on Monday.