PURPOSE: To obtain the humidity current converter which has high accuracy and enable signal delivery of long distance, by the constitution that the humidity detection section of the humidity converter and the signal output section are electrically isolated and the signal is delivered in current.

CONSTITUTION: The capacitor C of the RC integration circuit 2 acts like the humidity detector in which the electrostatic capacity of Al2O3 film is given as an exponential function to the relative humidity of the atmosphere. The time constant of this integration circuit is measured as the humidity information at the time constant measuring circuit 3 and the measuring signal is electrically isolated at the photo isolation circuit 4. The logical product circuit 6 takes the logical product between the circuits 4 and 5, the value of the relative humidity is output as pulse, which is counted at the counting circuit 7. This counting value is temporarily stored at the sample holding circuit 8, and this value is output externally from the VI converter 13 as the DC current. Thus, the humidity information with high accuracy can be delivered to a long distance without the effect due to noise signal.