The man, believed to be in his 70s, drove off the roundabout and rolled into a ditch.
Firefighters from Wokingham and Reading were called to the scene at about 10.30am, where they had to cut open the Volkswagen Transporter van to release the man.
An air ambulance flew the man to Oxford's John Radcliffe Hospital, where he was treated for facial injuries and a broken leg.
His pet dog was also travelling with him, and also suffered a broken leg.
Emergency services left the scene at about noon.