Patent ID: 7550975

Claim:
A portable information terminal apparatus equipped with a battery and a voltage source for generating a fixed voltage from the battery, comprising: a measurement unit for measuring an applied voltage by converting the applied voltage from analog to digital and outputting a measurement value according to the applied voltage; a changeover unit for selecting one of a plurality of voltages and applying the selected voltage to the measurement unit, where the plurality of voltages includes at least respective voltages of the battery and the voltage source; and a voltage value output unit for making the changeover unit select a fixed voltage generated by the voltage source, making the measurement unit measure the fixed voltage as a reference voltage, and obtain a first measurement value as a measurement result, generating calculation-use information based on the first measurement value and a voltage value of the reference voltage that is fixed, where the calculation-use information is for the purpose of calculating a voltage value from a measurement result of measurement unit, making changeover unit select a voltage by the battery, making the measurement unit measure the voltage of the battery and obtain a second measurement value as a measurement result, and calculating, and outputting, a voltage value of the battery by using the second measurement value and the calculation-use information.