[en] In experimental facilities to investigate a system integral-response and/or to verify fuel rod integrity of nuclear reactors, the electrical heater specially manufactured to simulate the real nuclear fuel rod with the same scale have been used in the core of the experimental facility. This type of the electrical heater, so-called 'simulated fuel rod', is a kind of a sheath heater which involves Nichrome coiled wire as a heat generation element in the metal cladding tube. An alternating current power is supplied for heat generation source in this heater and thin thermocouples were embedded on the cladding surface to measure the fuel surface temperature. It means that a switching regulator by silicon-controlled rectifier is used to control the AC electrical power and undesirable electrical noises are superimposed on the thermocouples' signals by the time variation of the heater current. Although a low-pass-filter with a low cut-off frequency was commonly applied to remove the noises in the previous steady-state experiment, the problem have arisen that a fast temperature transient could not be followed due to a time-delay accompanied by the filter in the transient experiment. In the present study, we reveal the noise characteristics and designed / manufactured the new noise reduction filter with to reduce the time delay one-tenth less than that in the previous simple filter. The time constant of this filter is less than 10 ms which is smaller than that of thin thermocouples determined by its heat capacity. It can be regarded as the response speed enough to the practical application. (author)