Abstract: A device for supporting deterioration determination includes: a first calculating unit that: acquires a dataset including a plurality of reaction condition values and a voltage in a first period and in a second period; and uses the dataset and a calculation formula to calculate a parameter group of the calculation formula for each period; a second calculating unit that substitutes a reaction condition value in the calculation formula in which the parameter group is incorporated to calculate a comparison target value for each period; and a third calculating unit that calculates a deterioration degree of the water electrolysis module based on a difference between a first comparison target value and a second comparison target value.