Parametric study on steam condensation in a heat transfer pipe in various condition has been executed considering evaluation of condensation behavior in Isolation Condenser (IC) equipped in BWR-3 which was operated in Fukushima Dai-ichi NPS as unit #1. Horizontally placed U-shaped heat pipe was installed in a large tank, and saturated steam was injected into the U-shaped heat pipe changing its flow rate. Temperature, pressure and flow rate in the experimental loop were measured. Especially for inside temperature of the heat pipe, 13 thermocouples were installed into the heat pipe from upward and downward individually with consideration of temperature change from saturated condition due to cooled water which originally appeared by condensation inside the heat pipe. Steam was supplied by electrical boiler of 50 kW, and installation of bypass line before the test section successfully avoided the effect of intermittent ON/OFF control of the electrical boiler. The apparatus was shaken down and confirmed about the accuracy of installed sensors or controllable range of the condensation condition inside the heat pipe, and at last widely varied conditions of condensation inside the heat pipe were observed and the availability of the apparatus was validated.