Abstract: A fluid heating apparatus is provided which comprises a heat-generating bent tube formed of an electrically conductive material in a tubular configuration and having opposite ends connected in communication to piping through which fluid to be heated is passed, a coil provided outside the heat-generating bent tube and wound to surround the heat-generating bent tube, and a power supply unit for feeding a high-frequency current through the coil. The fluid heating apparatus suppresses the generation of particles in the path of the fluid and may be used to heat gas or liquid in an apparatus for processing semiconductor substrates and flat panel substrates.