A hydrogen sensor includes a hydrogen-absorbing material, a thermoelectric element, an electrical circuit for driving the thermoelectric element, a thermometer for the hydrogen-absorbing material, a temperature control circuit for maintaining the hydrogen-absorbing material at a constant temperature using the thermoelectric element, a unit for calculating the exothermic value of the hydrogen-absorbing material based on the electrical current flowing from the drive circuit, and a unit for calculating the hydrogen uptake of the hydrogen-absorbing material based on the exothermic value.