manager's office; caretaker's room
Typically refers to the on-site office or room of a building manager, superintendent, or caretaker, especially in apartment buildings or condominiums.
Can I leave my luggage at the caretaker's room?
The apartment building's manager's office is next to the entrance on the first floor.
管理室 is a more general term for a management or control room, not necessarily for a residential building caretaker.
管理人 refers to the person (manager/caretaker), while 管理人室 is the room or office where they work.
Compound of 管理人 (かんりにん, 'manager, caretaker') + 室 (しつ, 'room').