Ex-IMF chief Dominique Strauss-Kahn, who denies charges of pimping, has told a court in northern France that he took part in only a few rare sex parties.
He said prosecutors had greatly exaggerated the frequency of his "licentious evenings". There had only been 12 in three years, he said.
Mr Strauss-Kahn is accused of helping procure sex workers for a prostitution ring based at a hotel in Lille.
He has argued that he did not know the women were prostitutes.
Although using prostitutes is not illegal in France, supplying them or assisting in supplying them is. Prosecutors have been quoted as saying Mr Strauss-Kahn, 65, played a pivotal role in facilitating the orgies, describing him as the "party king".
If found guilty, the one-time potential candidate for the French presidency could face up to 10 years in jail and a €1.5m (£1.13m) fine.
'He did it for fun'
As he took the stand on Tuesday, Mr Strauss-Kahn said: "I committed no crime, no offence."
"The prosecution gives the impression of unbridled activity," he told the court. But, he added: "There were only 12 parties in total - that is four per year over three years."
Mr Strauss-Kahn also denied organising the parties he took part in.
"I am in no way the organiser of these parties. I did not have the time to organise any party," he said.
As he arrived in court in Lille earlier, three topless protesters from the Femen activist group jumped on his car, with "pimps, clients, guilty" painted on their chests. They were taken away by police.
The former IMF chief - widely known by his initials DSK - is expected to give evidence for three days. He has not attended the trial since it opened on 2 February, when his appearance attracted international media attention.
The day before he was due to testify, an ex-prostitute named Mounia described how she had been paid €900 (£690) by a businessman, David Roquet, for what she had been told would be a "small party".
She told the court that she had been specifically chosen for Mr Strauss-Kahn and no-one else.
Mounia's evidence is expected to play an important part in the trial, as the prosecution tries to prove that he knew she and another woman, Jade, were prostitutes.
Mr Roquet, aged 46 and one of the men who organised the parties, said on Monday that he had taken part for "professional" purposes.
It was important for his construction business and it enabled him to have contact with Mr Strauss-Kahn, he told the court.
"He did it for fun. We had some lovely evenings," he told French radio earlier, adding that five or six couples would be involved.
Among the 13 co-accused are luxury hotel managers, a lawyer, a former police commissioner and a brothel owner nicknamed "Dodo the Pimp".
They face charges of "aggravated pimping" while the former head of the International Monetary Fund is accused of using his business contacts to hire women for sex parties in Paris, Lille and Washington.
It is the latest sex-related allegation to trouble Mr Strauss-Kahn, who stepped down from the IMF after being accused of attempted rape by a hotel maid in New York in 2011.
The case also ended his political career. Mr Strauss-Kahn - a Socialist former finance minister - was at the time widely regarded as a top contender for the French presidential election the following year.
The charges were eventually dropped and he reached a settlement with the maid, Nafissatou Diallo.
Two other cases against him, concerning allegations of sexual assault and gang rape, have already been dropped.