The present disclosure relates to a hydrogen gas production method including: a first step of generating a mixed gas containing hydrogen and carbon dioxide from a hydrogen storage agent by dehydrogenation reaction using a catalyst in a reactor; a second step of purifying the generated mixed gas to acquire a gas having a high hydrogen concentration; a third step of separating a solution in the reactor into a solution enriched with the catalyst and a permeate using a separation membrane unit; and a fourth step of supplying the solution enriched with the catalyst to the reactor for reusing in the first step.