[en] The Ex-Vessel Irradiation Rig (EXIR) is the on-line measurement and control irradiation equipment. It was developed to test uniaxial creep rupture strength of the reactor structural material under neutron irradiation condition, and installed between reactor guard vessel and safety vessel of the Experimental Fast Reactor 'JOYO'. The irradiation test using EXIR started at the 29th operation cycle in August 1994, and finished at the 30th operation cycle in March 1997 since the burst signals of two test pieces were detected. Through this irradiation test, performance of EXIR are confirmed and in reactor creep data on SUS316FR were obtained. The results are summarized as follows. (1) Temperature Conditions: The Temperature of the test pieces was controlled so as to be constant during the reactor operation. Its deviation from target temperature was recorded within ±2degC, which sufficiently outperformed the designed accuracy of ±3degC. (2) Tensile load Conditions: The control of the tensile load was retained in ±8.8N range for the set load value, and it was the performance which sufficiently satisfied control precision ±29.4N. (3) Displacement Result: On SUS316FR which was the structural material for fast reactor, uniaxial creep rupture strength test under the neutron irradiation was carried out, and the displacement data were acquired. The analysis of the displacement data will be reported after post irradiation experiment. (author)