A power management system, which manages a transaction of power generated based on renewable energy, includes: a power supply system capable of supplying power generated based on the renewable energy to a power demand system; and a power demand-supply management apparatus that manages demand and supply of the power. The power demand-supply management apparatus requests the power supply system to supply the power to the power demand system in a power generation time zone of the power, and issues, to the power demand system, a certificate that an amount of supplied power has been consumed in accordance with generation of the power.