A hydrogen gas sensor including a first electrode 3 provided on one surface of a proton conduction layer 1; a second electrode 5 provided on the other surface of the proton conduction layer 1 in opposition to the first electrode 3; and these components are supported in a support element including a first support element 9a and a second support element 9b. A conductive, elastic element 23 is disposed between a first lead portion 10a and a first electrode 3 in contact with the first lead portion 10a and the first electrode 3. The conductive, elastic element 23 is an electrically conductive, elastic sheetlike element made of metal, and has a pair of right-hand and left-hand through-holes 25 formed therein at a central portion thereof. The conductive, elastic element 23 is held between the first lead portion 10a and the first electrode 3 while being pressed inward by a first support element 9a. Thus, the first electrode 3 comes in close contact with the proton conduction layer 1, whereby electrical connection is established therebetween.