A quantum entangled photon pair generating device, an optical frequency dividing filter, a 2N-input/2N-output optical switch, a 2N number of quantum key receiving devices, an optical transmission path and a control unit are provided. The quantum entangled photon pair generating device generates quantum entangled photon pairs. The optical frequency dividing filter receives the quantum entangled photon pairs, divides an optical frequency region by 2N, and performs output. The 2N-input/2N-output optical switch allocates photons of the 2N number of optical frequency regions to any one of a 2N number of output ports, and outputs the photons. Each of the 2N quantum key receiving devices performs photon detection, uses a signal processing circuit of the quantum key receiving device to transmit measurement basis information to generate a quantum encryption key and to receive measurement basis information sent from the other quantum key receiving devices, and further, performs error correction and privacy amplification.