A solar thermal power generation system includes a solar heat collection system that generates superheated steam by solar heat, a main power generation system that performs power generation by part of the superheated steam generated by the solar heat collection system, a solar heat storage/release system that stores heat in a heat storage medium or releases the heat stored in the heat storage medium, and a secondary power generation system that performs power generation by saturated steam generated by the heat storage or the heat release in the solar heat storage/release system. The solar heat storage/release system includes a heat storage heater for exchanging heat between the rest of the superheated steam generated by the solar heat collection system and the heat storage medium to store heat in the heat storage medium and to generate saturated steam, a low-temperature tank for containing the heat storage medium to be supplied to the heat storage heater, and a high-temperature tank for containing the heat storage medium after the heat storage in the heat storage heater. The secondary power generation system includes a saturated steam turbine into which the saturated steam generated by the heat storage heater can be introduced.