In a signal processor for use in an electronic compass for controlling an offset voltage generated in an analog signal process and automatically controlling an amplification gain, an analog signal processor 52 amplifies signals Sx and Sy, and controls an offset voltage and amplitude A generated during an amplification process. An analog/digital (AD) converter 53 converts analog signals Vadcx and Vadcy from the analog signal processor 52 into a digital signal. A digital signal processor 54 measures a maximum value V_adc-max and a minimum value V_adc-min associated with the digital signal from the AD converter 53, and outputs, to the analog signal processor 52, an offset control signal Soc and a gain control signal Sgc based on the maximum value V_adc-max and minimum value V_adc-min. The signal processor can maintain levels of signals, to be inputted into the AD converter, to be within a reference voltage range.