A pipe joint (C; Ja; Jb; Jc; Jd; Je; Jf; Jg; Jh; Jk; Jm; Jn; Jp) which includes: a cylindrical joint body (16; 16b; 16e; 16f; 16g) into which a pipe is inserted and which is configured to be capable of communicating with a refrigerant flow path (17; 17g) of a heat exchanging unit (B, D); a cylindrical fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f) mounted to the joint body (16; 16b; 16e; 16f; 16g) by screwing; a ferrule receiving an axial pressing force from the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f) screwed in a clamping direction, thereby airtightly sealing a gap between an inner periphery of the joint body (16; 16b; 16e; 16f; 16g) and an outer periphery of the pipe; and a clamping nut capable of applying a rotative force in the clamping direction to the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f) when rotated by fitting a general-purpose tool to a fitting portion formed on an outer periphery thereof, characterized by: a loosening thread (68; 68d) formed on an outer periphery of the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f) and threaded in a direction opposed to a direction in which the joint body (16; 16b; 16e; 16f; 16g) and the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f) are threaded; and a screw-in preventing portion (39; 134) abutting against a loosening tool thereby to prevent further screw-in when the loosening tool is screwed into the loosening thread (68; 68d) and rotated in a direction opposed to a clamping direction of the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f). a cylindrical joint body (16; 16b; 16e; 16f; 16g) into which a pipe is inserted and which is configured to be capable of communicating with a refrigerant flow path (17; 17g) of a heat exchanging unit (B, D); a cylindrical fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f) mounted to the joint body (16; 16b; 16e; 16f; 16g) by screwing; a ferrule receiving an axial pressing force from the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f) screwed in a clamping direction, thereby airtightly sealing a gap between an inner periphery of the joint body (16; 16b; 16e; 16f; 16g) and an outer periphery of the pipe; and a clamping nut capable of applying a rotative force in the clamping direction to the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f) when rotated by fitting a general-purpose tool to a fitting portion formed on an outer periphery thereof, characterized by: a loosening thread (68; 68d) formed on an outer periphery of the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f) and threaded in a direction opposed to a direction in which the joint body (16; 16b; 16e; 16f; 16g) and the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f) are threaded; and a screw-in preventing portion (39; 134) abutting against a loosening tool thereby to prevent further screw-in when the loosening tool is screwed into the loosening thread (68; 68d) and rotated in a direction opposed to a clamping direction of the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f). a loosening thread (68; 68d) formed on an outer periphery of the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f) and threaded in a direction opposed to a direction in which the joint body (16; 16b; 16e; 16f; 16g) and the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f) are threaded; and a screw-in preventing portion (39; 134) abutting against a loosening tool thereby to prevent further screw-in when the loosening tool is screwed into the loosening thread (68; 68d) and rotated in a direction opposed to a clamping direction of the fixing member (35; 66a; 66b; 66c; 66d; 66e; 66f).