A distribution grid management apparatus that is a power generation amount estimation apparatus includes a communication unit to acquire a solar radiation amount that is a measurement value measured by a solar radiation meter at an interval shorter than a data collection interval that is an interval at which a measurement value from a smart meter that measures the amount of electric power is collected; and a power generation amount calculation unit to estimate, on the basis of the solar radiation amount, the power generation amount of each of a plurality of photovoltaic facilities connected to a distribution line of a high-voltage grid.