noun
basement floor; underground floor
Refers to a floor level below ground, such as B1, B2, etc. Antonym: 地上階 (above-ground floor).
Antonyms: 地上階
このビルの地下階には駐車場があります。
There is a parking lot on the basement floor of this building.
地下階へはエレベーターで降りてください。
Please take the elevator down to the basement floor.