Cavallo was arrested in Mexico in 2000 on the orders of Baltazar Garzon, one of Spain's top criminal judges.
In 2003 he was extradited to Spain, which accuses him of having
participated in 227 kidnappings and acts of torture involving 110
people in Argentina, according to the AFP news agency reported.
Argentina asked for him to to be returned to the country in relation to alleged atrocities committed by a secret unit of the country's notorious Navy Mechanics School in Buenos Aires, which kidnapped and tortured people during the "Dirty War".
Cavallo denies all the charges.
More than 5,000 of the roughly 30,000 people who disappeared
under the military government are thought to have passed through the detention centre.
Garzon had sought Cavallo's arrest under the principle of
"universal jurisdiction" under international law, which makes atrocities
committed in one country subject to prosecution by other countres' courts.
Carvallo's extradition to Spain marked the first time a country had extradited a suspect to another to stand trial for alleged rights abuses committed in a third.