A gas filling apparatus in the gas filling system includes a precooler for cooling hydrogen gas supplied from the gas supply source (11) and discharges the hydrogen gas cooled by the precooler to fill the hydrogen gas into the gas tank. The temperature of the hydrogen gas cooled by the precooler is detected by a gas temperature sensor that detects, upstream of the gas tank, a temperature of the hydrogen gas cooled by the precooler. A flow rate controller controls a filling flow rate of the hydrogen gas to be filled into the gas tank, based on the detected temperature of the hydrogen gas. For example, when the detected temperature of the hydrogen gas is high, the filling flow rate is reduced as compared to that when the detected temperature of the hydrogen gas is lower.