1In Japanese, 'mansion' means a mid- or high-rise reinforced-concrete apartment/condominium building — either owned or rented. This is a 'wasei-eigo' (Japanese-made English) usage that differs from the English word 'mansion' (a large house).
彼は先月、駅前のマンションに引っ越した。
He moved into an apartment near the station last month.
このマンションは駅から近くて便利だ。
This apartment building is conveniently close to the station.
マンションの管理費は毎月2万円かかる。
The apartment's management fee costs 20,000 yen every month.
将来は一戸建てより、便利なマンションに住みたい。
In the future, I'd rather live in a convenient apartment than a detached house.