Dozens of prisoners, mostly Sunni Arabs, were being kept in cramped rooms, Aljazeera's correspondent reported. Some have been in prison for years.
The prisoners collapsed and cried when they saw a camera, hoping that their plight would at last be known by people all over the world, the correspondent said.
In the video aired on Monday, prisoners described their torture, which included electric shocks. Some showed scars on their bodies as evidence of abuse.
Many of the prisoners, aged between 20 and 60, said they were taken from the streets or their work places, with no charges filed against them.
They said they were forced, under torture, to sign confessions that they had committed serious crimes.
The jail is near the Iraqi Interior Ministry in Baghdad.
The Iraqi government said that it would investigate the reports.
Prisoners said they were forced
to sign confessions
About 65 of the prisoners were released after the video was aired, but 75 others were transferred to another jail.
The correspondent said the jail is probably one that Iraqi government investigators have not visited.
Also on Monday, an empty minibus loaded with explosives
blew up near a hospital in east Baghdad, killing three people and wounding 13.
Other violence in and around Baghdad on Monday killed another six people and injured 21.
Lieutenant Mohammed Khayoun of the Baghdad emergency police said the minibus exploded near the al-Kindi hospital and east Baghdad's Nadhaa bus station. The driver of the van abandoned it on the street and ran, he said.
All three killed were Iraqi civilians, and the wounded included five police officers, he said.
In Baghdad, police said that a number of clashes between unidentified armed men, police and the Iraqi army resulted in the death of two police officers and injuries to another nine.