Police are investigating a robbery, which took place at an Asda store in Pontprennau on Saturday afternoon.
Thousands of pounds was stolen when the driver of a G4S security van was targeted by a man at around 12.50pm.
Police said the victim was "left shaken but unharmed" by the incident.
The suspect is a white man who was wearing a navy tracksuit with white stripes along the side.
Police are asking anyone with information to call 101 or Crimestoppers anonymously on 0800 555 111.