Apparatus for humidity detection comprises a humidity sensing element, the electrostatic capacitance of which varies in accordance with the ambient humidity, a fixed capacitor, first and second pulse generating circuits respectively responsive to the sensing element and the capacitor, and a computing circuit responsive to pulses from the first and second pulse generating circuit. The sensing element and the fixed capacitor are respectively charged via resistors to produce first and second pulses in accordance with voltage across the sensing element and the capacitor. The difference between the widths of the first and second pulses is detected in the computing circuit to produce an output pulse indicative of the relative humidity, thereby compensating for undesirable infuenece due to dielectric loss in the sensing element so as to accurately measure humidity irrespectively of the ambient temperature.