A fuel supply apparatus that supplies fuel to an internal combustion engine by injecting liquid fuel from a fuel injection valve into a suction port is configured by a microbubble generator that generates microbubbles and an ultrasonic wave generator that generates an ultrasonic wave depending on a gas in the microbubbles generated by the microbubble generator. In the fuel supply apparatus, the generated microbubbles are mixed into the liquid fuel that is supplied to the fuel injection valve, and the liquid fuel in which the microbubbles are mixed is irradiated with the ultrasonic wave depending on the driving state of the internal combustion engine. When the liquid fuel in which the microbubbles are mixed is irradiated with the ultrasonic wave, a temperature of the liquid fuel is raised instantaneously due to contraction of the microbubbles.