A foldable pedal apparatus for a vehicle includes a manual driving mode of the vehicle in which a driver drives a vehicle manually, and a pedal pad protrudes from a pedal casing and enters a pop-up state where the pedal pad is exposed toward the driver, and an autonomous driving mode of the vehicle in which the driver does not drive, and the pedal pad is retracted into the pedal casing and enters a hiding state where exposure of the pedal pad toward the driver is prevented. An interior design of the vehicle is optimized by allowing the pedal pad to pop up through a panel hole formed on a footrest panel when the pedal pad changes from the hiding state to the pop-up state.