1. A device for detecting hydrogen concentration comprising: a first heat-generating resistor of which a first electrophysical quantity varies depending upon the hydrogen concentration; a second heat-generating resistor neighboring said first heat-generating resistor in a direction of the gas flow and of which a second electrophysical quantity varies depending upon the hydrogen concentration as does said first electrophysical quantity; and concentration detector means for detecting the concentration of hydrogen based on said first electrophysical quantity and said second electrophysical quantity; wherein said concentration detector means includes: amount-of-change calculation means for calculating the amount of change in a target physical quantity, which is either said first electrophysical quantity or said second electrophysical quantity; correction amount calculation means for calculating the correction amount based on a difference between said first electrophysical quantity and said second electrophysical quantity; and concentration calculation means for calculating the concentration of hydrogen based on a difference between said amount of change and said correction amount.