According to an embodiment, a quantum key distribution device includes a sharer, a key distillation processor, a first manager, and a second manager. The sharer is configured to share a photon string with the another quantum key distribution device using quantum key distribution via a quantum distribution channel, and obtain a photon bit string corresponding to the photon string. The key distillation processor is configured to generate a link key from the photon bit string. The first manager is configured to store the link key as a link transmission key. The second manager is configured to store, in a storage, a first application key from an application key to be used in cryptographic data communication, encrypt a second application key from the application key, using the link transmission key, and send the encrypted second application key to another quantum key distribution device via a classical communication channel.