A foldable mobile electronic device is provided. The foldable mobile electronic device includes a processor configured to recognize, based on the data received from the first sensor, a change in a state of the foldable mobile electronic device from the folded state to a partially folded state before reaching an unfolded state, to identify a first illuminance by using the data received from the second sensor, based on the recognized state change, to set a first luminance corresponding to the first illuminance as a brightness of the display, to when an angle identified after the state change falls within a predetermined first angle range or when a specific time has not elapsed after the state change, perform a real-time adjustment operation on the brightness of the display, based on a second illuminance identified using the second sensor, and to when the angle identified after the state change is outside the first angle range or when the specific time has elapsed after the state change, perform a hysteresis adjustment operation on the brightness of the display, based on the first illuminance.