A fuel supply apparatus for an internal combustion engine includes: a feed pump capable of feeding a fuel of the internal combustion engine; a high pressure fuel pump that pressurizes the fuel fed from the feed pump; and a second injector that supplies the pressurized high-pressure fuel to the internal combustion engine selectively. An ECU of the fuel supply apparatus includes: a pulsation width detection unit that detects a pulsation width in a pressure of the fuel fed from the feed pump to the high pressure fuel pump; and a feeding condition determination unit that determines that a condition variation causing fuel vapor to form in the fuel fed to the high pressure fuel pump has occurred when the pulsation width detected by the pulsation width detection unit falls rapidly to a preset threshold variation width.