Heat-resistant in-vessel components, i.e., a heat sink, a front-end optics housing, and a diagnostic window have been designed in terms of heat-handling capability and thermal stress and mechanical stress by using a finite element method code. The heat sink, which is exposed to a plasma heat flux of up to 0.3 MW/m2, consists of carbon tiles, a carbon sheet, and a stainless steel heat sink with a water-cooling channel. Analysis shows that at a water flow rate of 0.9 kg/s with a water pressure of 0.5 MPa, an increase in the carbon tile temperature is mitigated below the limit related with detrimental red-hot (900°C). The front-end optics housing temperature and the diagnostic window of sapphire glass temperature are within the allowable temperature. The thermal stress and mechanical stress are less than the allowable value, respectively.