A humidity sensing apparatus which includes a humidity sensor which detects humidity as a function of impedance is provided. A reference resistor has a predetermined resistance value. A charge switching circuit selectively couples one of the reference resistor or the humidity sensor in series with a reference capacitor which has a predetermined capacitance. A voltage judging circuit determines whether the terminal voltage of the reference capacitor is high or low. A charge/discharge switch selectively charges and discharges the reference capacitor in accordance with the output of the voltage judging circuit. A sensor direction switching circuit inverts the direction of current flowing through the humidity sensor during charging of the reference capacitor. An oscillation frequency counter counts the number of charge/discharge cycles which are repeated during a predetermined time period. A humidity sensor resistance value calculating circuit calculates the resistance value of the humidity sensor in accordance with the number of repeated charge/discharge cycles when the reference capacitor is coupled to the reference resistor for charging and the number of repeated charge/discharge cycles when the reference capacitor is coupled to the humidity sensor during charging. A humidity determining circuit determines the humidity from the resistance value of the humidity sensor calculated by the humidity sensor resistance value calculating circuit.

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