noun
walk-in closet; wardrobe room; dressing room; costume room
A room used for storing clothes, changing, or keeping costumes. Can refer to a walk-in closet, a backstage costume room, or a dedicated dressing area.
新しい家には広い衣装部屋がある。
The new house has a spacious walk-in closet.
劇場の衣装部屋で衣装を選んだ。
I chose a costume in the theater's costume room.
Compound of 衣装 (いしょう, 'clothing, costume') and 部屋 (へや, 'room'). The reading いしょうべや follows standard rendaku voicing of へや to べや in compounds.