Abstract: The present invention discloses a solar-charged warning device, mounted on a helmet, including at least one light-emitting element, a solar photovoltaic panel, a voltage amplifier circuit, a sensor circuit, a charge/discharge circuit, and a secondary battery. The solar photovoltaic panel mounted on the helmet is used to absorb the solar energy and transform thereof into the electricity, and then the electricity is inputted into the sensor circuit, the charge/discharge circuit and the secondary battery, for storing the electricity in the secondary battery. When there needs the electricity, it can be discharged by the charge/discharge circuit and then amplified by the voltage amplifier circuit to reach the required voltage, so as to drive the light-emitting element to shine. When there exists the light source, the secondary battery will be charged. When in the dark, the electricity stored in the secondary battery will be discharged to drive the light-emitting element to shine.