A foldable pedal device for an autonomous vehicle is provided. In a manual driving mode, in which the driver directly operates the vehicle, a pedal pad rotates backwards and pops up in a passenger compartment space to allow the driver to manipulate the pedal pad. In an autonomous driving mode, in which the driver does not directly operate the vehicle, the pedal pad rotates forwards and is hidden in an engine compartment space to be prevented from being exposed to the passenger compartment space and from being manipulated by the driver.