Abstract: In a typical method of separating isotopes, a linear material is fed between electrodes arranged in a vacuum vessel. Joule heat is generated by supplying a current to the linear material. A vapor flow is produced by heating and evaporating the linear material. Only a specific isotope in the vapor flow is selectively ionized by radiating a laser beam on the vapor flow. The ionized isotope is separated by using at least one of electric and magnetic fields. A typical isotope separating apparatus includes a vacuum vessel, a material feeder, a power source system, a laser optical system, and an ion separating unit. The material feeder feeds a linear material containing a plurality of types of isotopes between electrodes in the vacuum vessel. The power source system supplies a current to the linear material to heat and evaporate it.