I eat kcal, do I also burn kcal or cal?

Hi, I live in Europe. When I eat 100g of chocolate I consume about 500 kcal but when I go to the gym the treadmill shows I burn calories, for example 300 calories in 30 minutes. I know there are 1000 calories in 1 kcal and it confuses me a bit. Can someone please explain to me how this works and if the treadmill really shows calories but not kcal.