safety-deposit company; custodian company
A company that provides safe storage or custody services for valuables, documents, or assets.
This safety-deposit company specializes in storing valuables.
倉庫会社 is a warehousing company that stores goods in general, while 保管会社 emphasizes safekeeping and custody services, often for valuables or documents.
Compound of 保管 (ほかん, 'safekeeping, custody') and 会社 (がいしゃ, 'company').