When you go to see a doctor, you are some kind of sick.
But Japanese go to see a doctor even they feel good.
To prevent expected illness or to find illness, some people have a complete medical checkup, especially when we reach 40s.
Of course there are many people who never take the exam too.
We can choose the contents of the exam, for example, lung cancer test for smoking person, MR (Magnetic resonance imaging) of a head for person who has migraine.
It costs a lot so many people take it once in 2~3years but some people who have some trouble of their health take the exam every year.