A hydrogen gas filling device includes a reception circuit, a difference calculation circuit, a filling speed calculation circuit, an accumulator, and a filing machine. The reception circuit is configured to receive, from a vehicle equipped with a tank to be filled with hydrogen gas and powered by the hydrogen gas, a value of a parameter of the vehicle. The difference calculation circuit is configured to calculate a difference between a predetermined value and the value of the parameter received from the vehicle. The filling speed calculation circuit is configured to calculate a filling speed of the hydrogen gas depending on the difference. The accumulator is configured to accumulate hydrogen gas. The filling machine is configured to fill the tank with the hydrogen gas from the accumulator at the calculated filling speed. A hydrogen gas filling method includes the operations noted above.