A load sensor includes a optical fiber sensor that provides output analog signals in response to shocks of various magnitudes caused by hits by a vehicle on various objects, two or more amplifiers each of which approximates a non linear function of the analog signals and a unit that converts the linear functions into digital data. Therefore, each analog signal either in a lower magnitude range or a higher magnitude range can be amplified by one of the amplifiers that has a more suitable gain, so that the magnitude of the shock can be accurately converted into digital data for a pedestrian protection airbag system.