An encryption method comprising: a first modulation step of associating M/2 sets of pairs of states, each pair of states having a state "0" and another state "1", with M/2 different first integer values, respectively, and associating all of the states "0" and "1" of the M/2 sets of pairs of states with M different second integer values, respectively, where M is an even number which is twice an odd number, generating a pseudo random number, r i, that has any one of the M/2 different first integer values for each bit of plaintext, x i, assigning, for each bit of plaintext x i, as a specific pair of states, a pair of states having a first integer value of the M/2 different first integer values same as a value generated as the pseudo random number r i from among the M/2 sets of pairs of states, and outputting, as a modulation output value, s i ', of each bit of plaintext x i, a second integer value of the M different second integer values associated with the state of each bit of plaintext x i in the specific pair of states assigned for each bit of plaintext x i; and a second modulation step of generating a physical random number, f i, that has any one of a predetermined number of different third integer values for the modulation output value s i ' of the first modulation step, adding the physical random number f i to the modulation output value s i ', finding a residue when a sum of the modulation output value s i ' and the physical random number f i is divided by the number M, associating the residue with any one of other second integer values, and outputting the any one of other second integer values as encrypted data of each bit of plaintext x i, wherein in order to discriminate the state of the specific pair of states by the demodulation pseudo random number r i in a cryptogram decoding side, the predetermined number and the third integer values are set so that a first range, A i, which is a set of the other second integer values obtained by modulating the second integer value s i ' set for one state of each pair of states in the second modulation step and a second range, B i, which is a set of the other second integer values obtained by modulating the second integer value s i ' set for another state of each pair of states in the second modulation step, do not overlap. a first modulation step of associating M/2 sets of pairs of states, each pair of states having a state "0" and another state "1", with M/2 different first integer values, respectively, and associating all of the states "0" and "1" of the M/2 sets of pairs of states with M different second integer values, respectively, where M is an even number which is twice an odd number, generating a pseudo random number, r i, that has any one of the M/2 different first integer values for each bit of plaintext, x i, assigning, for each bit of plaintext x i, as a specific pair of states, a pair of states having a first integer value of the M/2 different first integer values same as a value generated as the pseudo random number r i from among the M/2 sets of pairs of states, and outputting, as a modulation output value, s i ', of each bit of plaintext x i, a second integer value of the M different second integer values associated with the state of each bit of plaintext x i in the specific pair of states assigned for each bit of plaintext x i; and associating M/2 sets of pairs of states, each pair of states having a state "0" and another state "1", with M/2 different first integer values, respectively, and associating all of the states "0" and "1" of the M/2 sets of pairs of states with M different second integer values, respectively, where M is an even number which is twice an odd number, generating a pseudo random number, r i, that has any one of the M/2 different first integer values for each bit of plaintext, x i, assigning, for each bit of plaintext x i, as a specific pair of states, a pair of states having a first integer value of the M/2 different first integer values same as a value generated as the pseudo random number r i from among the M/2 sets of pairs of states, and outputting, as a modulation output value, s i ', of each bit of plaintext x i, a second integer value of the M different second integer values associated with the state of each bit of plaintext x i in the specific pair of states assigned for each bit of plaintext x i; and a second modulation step of generating a physical random number, f i, that has any one of a predetermined number of different third integer values for the modulation output value s i ' of the first modulation step, adding the physical random number f i to the modulation output value s i ', finding a residue when a sum of the modulation output value s i ' and the physical random number f i is divided by the number M, associating the residue with any one of other second integer values, and outputting the any one of other second integer values as encrypted data of each bit of plaintext x i, wherein in order to discriminate the state of the specific pair of states by the demodulation pseudo random number r i in a cryptogram decoding side, the predetermined number and the third integer values are set so that a first range, A i, which is a set of the other second integer values obtained by modulating the second integer value s i ' set for one state of each pair of states in the second modulation step and a second range, B i, which is a set of the other second integer values obtained by modulating the second integer value s i ' set for another state of each pair of states in the second modulation step, do not overlap.