internist; physician (internal medicine)
A doctor specializing in internal medicine; distinct from a surgeon (外科医) or general practitioner.
内科医に診てもらったほうがいいですよ。
You should see an internist.
彼は大学病院の内科医として働いている。
He works as an internist at a university hospital.
医者 is a general term for doctor; 内科医 specifies the field of internal medicine.
外科医 treats patients through surgery, whereas 内科医 treats internal illness through non-surgical, medical means.
Compound of 内科 (internal medicine) and 医 (doctor).