The camera at the junction of Cardiff's Newport Road and Colchester Avenue snapped motorists going through the red light or breaking the 30mph limit.
It caught over three times as many drivers as the next busiest camera - North Road, Cardiff, which had 3,836.
All but one of the ten most prolific Welsh speed cameras are in south Wales.
Figures which show the number of drivers caught speeding by fixed speed cameras on Welsh roads have been released by the GoSafe Partnership - which is made up of local councils, Welsh police forces and the Welsh government.
The camera topping the list on Newport Road, one of the busiest roads in Cardiff - saw 12,107 motorists caught between April 2014 and March 2015, an average of more than 30 a day.
This would generate an estimated Â£3,000 each day in Â£100 fixed penalty notices issued to drivers exceeding the 30mph limit.
But Chris Hume, partnership manager at GoSafe, which is responsible for red light and speed camera enforcement, insisted the camera was helping with safety.
"This camera has been there since 2011. The collision history on the 50m stretch of road there in the three years before that was that there were 10 collisions which caused injuries - two of them involved pedestrians," he said.
"Since the camera has been there we have had three collisions.
"That suggests the camera needs to be there. We're talking about one of the busiest arterial roads into Cardiff which has about 36,000 vehicles a day. So only one in every 1,000 drivers are doing something wrong."
He said the cameras were not being used to generate money for councils or police forces, with all the revenue from fines going to the UK government.
Last year, the Newport Road speed camera was dubbed the "UK's busiest" after it was revealed it was catching more drivers than a speed camera on the M60 in Greater Manchester.
Top 10 busiest permanent speed cameras in Wales
Source: GoSafe Partnership
More than 12,000 drivers have been caught by Wales' busiest speed camera in a year - but an expert says it is helping prevent accidents.