In Japanese usage, 'mansion' refers to a mid- or high-rise condominium/apartment building (often concrete construction). Similar to 'apartment' or 'condominium' in English, but with Japanese nuances.
彼は都心のマンションに引っ越した。
He moved into a condominium in the city center.
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が毎月かかる。
Apartment management fees are charged every month.