1. A urea synthesis process comprising reacting ammonia with carbon dioxide at a urea synthesis temperature and a urea synthesis pressure in a urea synthesis column, heating the resultant urea synthesis solution comprising urea, unreacted ammonia, unreacted carbon dioxide and water in a stripper at a pressure substantially equal to the urea synthesis pressure while bringing said solution into contact or no contact with at least part of feed carbon dioxide or feed ammonia to separate said unreacted ammonia and said unreacted carbon dioxide as a gaseous mixture of ammonia, carbon dioxide and water, treating further the urea synthesis solution containing unseparated unreacted ammonia and unreacted carbon dioxide to obtain urea, separately introducing the gaseous mixture separated in said stripper into a condenser having a tubular cooler to bring the mixture into contact with an absorption medium under cooling, thereby condensing said gaseous mixture, and recycling the thus-obtained condensate to the urea synthes
