A capacitive humidity sensor includes: a humidity sensing element with a humidity sensitive film and electrodes; and a processing circuit. The film has a dielectric constant variable in accordance with moisture. The electrodes detect capacitance of the film and outputs a signal corresponding to the capacitance. The processing circuit processes the signal. The film is made of inorganic material having fine pores for adsorbing the moisture. A diameter of the fine pores is set to be a predetermined diameter so that capillary tube aggregation phenomenon occurs at a predetermined relative humidity. The capacitance of the film has a change rate with respect to the relative humidity. The change rate in case of the relative humidity higher than the predetermined relative humidity is larger than that in case of the relative humidity lower than the predetermined relative humidity.