also: いしつぶつとりあつかいしょ
noun
lost and found office
A facility, typically in stations or public buildings, where lost items are collected and returned.
駅の遺失物取扱所で忘れ物を受け取った。
I picked up my lost item at the station's lost and found office.
忘れ物 refers to the lost item itself, while 遺失物取扱所 is the office that handles such items.
Compound of 遺失物 (lost property) + 取扱所 (handling office).