In a solar power generation control device, a memory stores an output voltage at which maximum power is obtained, for each illuminance on a panel surface of a solar panel, acquisition circuitry acquires a vehicle speed, a present illuminance on the panel surface, and first information indicating an illuminance in a prescribed area ahead of a vehicle, and calculation circuitry calculates a predicted illuminance on the panel surface, which is an illuminance after a lapse of a prescribed length of time, based on the first information and the vehicle speed. When determining that an absolute value of a difference between first and second output voltages, at which maximum powers are obtained respectively at the present and predicted illuminances, exceeds a prescribed threshold, control circuitry makes correction such that an output voltage of the solar panel coincides with the second output voltage upon the lapse of the prescribed length of time.