A vehicle includes an acceleration sensor that generates an output of an acceleration in a direction of the acceleration sensor. The output of the acceleration includes information on an orientation of the acceleration sensor relative to the vehicle. A method for determining an orientation of the vehicle includes (i) detecting a first output of the acceleration sensor; (ii) memorizing the first output as a reference orientation value, (iii) correcting the memorized reference orientation value, based on an average of outputs generated by the acceleration sensor while the vehicle travels after the first output is generated; and (iv) determining an orientation of the vehicle when the vehicle travels, based on the corrected reference orientation value and a second output of the acceleration sensor.