To provide a hydrogen sensor in which starting time is shortened without causing any damage onto a hydrogen detection element due to temperature rise in starting.

A hydrogen detection element 6 comprising a proton conductive solid oxide and a pair of electrodes provided on the opposite sides thereof, a first heater 5 for heating the hydrogen detection element 6, and a second heater 7 are encased in a case 1 having a hydrogen inlet 2 at least in the lower surface thereof. A gap is provided between the hydrogen detection element 6 and the first and second heaters 5 and 7 and the outer circumferential area of the first and second heater 5, 7 is set larger than that of the hydrogen detection element 6.