A Yuen encryption optical transmission device for implementing Y-00 protocol according to an optical intensity modulation format, comprising: a transmission information data sequence randomization device for generating transmission information by dividing input information into one or more blocks, appending a sequence number to the blocks and packetizing the same, and using the output sequence of an electrical noise generator to randomize and sort the sequence of the packets; a pseudorandom bit generation unit for generating pseudorandom bit sequence from an initial key; a base selection control unit for holding a base group configured by a number of bases and selecting one base from the base group in conformity with pseudorandom bits sequence; and an intensity optical modulation unit for using two optical intensities corresponding to the one selected base to generate an optical modulation signal based on the transmission information, wherein in all of the bases constituting the base group, the two optical signal intensities corresponding to each of the bases have values above and below an interposed intermediate point of a maximum intensity and a minimum intensity, the intensities of a signal group above the intermediate point being deployed concentrated around an optical intensity sufficiently spaced apart from the intermediate point and the intensities of the signal group below the intermediate point being deployed concentrated in the vicinity of an optical intensity sufficiently spaced apart from the intermediate point, and the range of intensities where the intensities of the signal group above the intermediate point and of the signal group below the intermediate point are respectively deployed in concentration is set so as to be entirely hidden by quantum shot noise appearing in proportion to the energy in the vicinity of the intensities of the signal group. a transmission information data sequence randomization device for generating transmission information by dividing input information into one or more blocks, appending a sequence number to the blocks and packetizing the same, and using the output sequence of an electrical noise generator to randomize and sort the sequence of the packets; a pseudorandom bit generation unit for generating pseudorandom bit sequence from an initial key; a base selection control unit for holding a base group configured by a number of bases and selecting one base from the base group in conformity with pseudorandom bits sequence; and an intensity optical modulation unit for using two optical intensities corresponding to the one selected base to generate an optical modulation signal based on the transmission information, wherein in all of the bases constituting the base group, the two optical signal intensities corresponding to each of the bases have values above and below an interposed intermediate point of a maximum intensity and a minimum intensity, the intensities of a signal group above the intermediate point being deployed concentrated around an optical intensity sufficiently spaced apart from the intermediate point and the intensities of the signal group below the intermediate point being deployed concentrated in the vicinity of an optical intensity sufficiently spaced apart from the intermediate point, and the range of intensities where the intensities of the signal group above the intermediate point and of the signal group below the intermediate point are respectively deployed in concentration is set so as to be entirely hidden by quantum shot noise appearing in proportion to the energy in the vicinity of the intensities of the signal group.