The camera on a 30mph limit junction of Newport Road  is catching an average of 71 speeding drivers every day.
A survey last year found a camera on the M60 in Greater Manchester caught about 26 speeding drivers per day.
The GoSafe partnership, which runs the Cardiff camera, said 99.5% of drivers at the site met the speed limit.
It said: "Motorists should comply with the relevant speed limit, which is there for a reason."
The body also insisted that placing cameras at a location was always "a last resort".
"The revenue from speeding fines is returned back to the government and not the partnership," said Chris Hume from GoSafe.
"There is a simple message - cameras are in place to save lives not to make money."
The camera was installed in 2012, but only went into fully commissioned operation earlier this year.
It has now notched up a staggering 13,624 penalty notices for speeding - and a further 146 drivers were caught for red-light offences.
A speed camera in Cardiff is the busiest in Britain - catching almost three times as many drivers each day as one on a busy Manchester motorway.