An encryption communication method comprising: the step a of causing an application (A11x) to transmit a data packet in which a loopback address serving as an IP address for closed communication in a self node (A1a) is set as a destination address, the application (A11x) executing encryption communication with another node apparatus (C1, D1) connected to a network; and the step b of causing a communication encryption module (A13a) operating as an independent process to receive the data packet having the loopback address set as the destination address and transmitted from the application (A11x), read out a communication partner IP address corresponding to the loopback address set as the destination address of the data packet from a first encryption communication path setting table (A132a) that holds a plurality of correspondences between the communication partner IP address and the loopback address, rewrite the destination address of the data packet to the readout communication partner IP address, and encrypt and transmit the data packet, characterized by further comprising: the step c of causing a communication method resolution unit (A122a) to determine on the basis of a domain name contained in one of a name resolution query transmitted from the application (A11x) to resolve an IP address of said other node (C1, D1) and a name resolution response as a response to the name resolution query whether said other node apparatus (C1, D1) is an encryption communication target node; the step d of causing an encryption communication path setting unit (A123a) to register, in the first encryption communication path setting table (A132a), a correspondence between the IP address of said other node apparatus (C1, D1) and a loopback address that is not used in any other communication session when said other node apparatus (C1, D1) is the encryption communication target node; and the step e of causing a name resolution query/response transmission/reception unit (A121a) to replace the IP address of said other node apparatus (C1, D1) contained in the name resolution response with the loopback address in the correspondence and transmit the name resolution response to the application (A11x), wherein the step a and the step b are executed after the step c, the step d, and the step e. the step a of causing an application (A11x) to transmit a data packet in which a loopback address serving as an IP address for closed communication in a self node (A1a) is set as a destination address, the application (A11x) executing encryption communication with another node apparatus (C1, D1) connected to a network; and the step b of causing a communication encryption module (A13a) operating as an independent process to receive the data packet having the loopback address set as the destination address and transmitted from the application (A11x), read out a communication partner IP address corresponding to the loopback address set as the destination address of the data packet from a first encryption communication path setting table (A132a) that holds a plurality of correspondences between the communication partner IP address and the loopback address, rewrite the destination address of the data packet to the readout communication partner IP address, and encrypt and transmit the data packet, the step c of causing a communication method resolution unit (A122a) to determine on the basis of a domain name contained in one of a name resolution query transmitted from the application (A11x) to resolve an IP address of said other node (C1, D1) and a name resolution response as a response to the name resolution query whether said other node apparatus (C1, D1) is an encryption communication target node; the step d of causing an encryption communication path setting unit (A123a) to register, in the first encryption communication path setting table (A132a), a correspondence between the IP address of said other node apparatus (C1, D1) and a loopback address that is not used in any other communication session when said other node apparatus (C1, D1) is the encryption communication target node; and the step e of causing a name resolution query/response transmission/reception unit (A121a) to replace the IP address of said other node apparatus (C1, D1) contained in the name resolution response with the loopback address in the correspondence and transmit the name resolution response to the application (A11x), wherein the step a and the step b are executed after the step c, the step d, and the step e.