Hi Tuongvan,
As Philip and RayH pointed out, there are many possibilities. Here is one system for you to consider:
A Registrar's Office
/ Office of the Registrar includes:
1. The Admission Department / Office is responsible for class registration and scheduling
activities.
2. The Transcript Department / Office
provides students access to their academic records.
3. The Verification Department /
Office provides verification of the student's status of enrollment, graduation,
and degrees conferred / awarded.
4. The Graduation Department / Office
provides services related to graduation and diplomas.
A person who works in the registrar office is called a registrar.
A person who works in the admission department / office is called either a
registrar or admission officer. However, the latter is more specific.
Again, please note that not every school follows this set up. In some schools, "the registration office" and "the admission office" can be used interchangeably.