A humidity sensor includes: a substrate; a pair of electrodes on the substrate; a humidity sensitive member between the electrodes having a capacitance changeable in accordance with humidity; an output element connecting to the electrodes in order to detect a capacitance of the humidity sensitive member and outputting a signal corresponding to the capacitance; and a setting member for setting a maximum amount of moisture in the humidity sensitive member to be a standard maximum amount of moisture. The humidity sensitive member is capable of absorbing a moisture up to the maximum amount of moisture. The setting member includes at least one of an element for reducing the maximum amount of moisture and an element for increasing the maximum amount of moisture.