According to an embodiment, a quantum key distribution (QKD) device includes a sharing unit, a correcting unit, a deciding unit, a calculator, and a privacy amplifier. The sharing unit is configured to generate a shared bit string through quantum key distribution with each other QKD device connected via quantum communication channels. The correcting unit is configured to generate a corrected bit string through an error correction process on the shared bit string. The deciding unit is configured to calculate an error rate in the corresponding quantum communication channel with respect to each other QKD device, and decide on a combined error rate from error rates calculated. The calculator is configured to calculate, based on the combined error rate, a length of an encryption key to be shared. The privacy amplifier is configured to generate the encryption key having the calculated length of the encryption key from the corrected bit string.