To provide a hydrogen gas sensor capable of detecting hydrogen gas and measuring a hydrogen gas concentration by a simple structure without requiring application of reference gas or voltage, and to provide a coin cell type hydrogen gas sensor using the hydrogen gas sensor.

In the hydrogen gas sensor configured by laminating a first electrode 11 and a second electrode 12 through a solid electrolyte film 13, the first electrode 11 and the second electrode 12 contain metal having catalysis capable of dissociating hydrogen to protons, the film thickness of the first electrode 11 is 1 to 25 nm, and the film thickness of the second electrode 12 is thicker than the film thickness of the first electrode 11.