A hydrogen gas filling method includes: a step for acquiring a pre-supply upstream pressure that is a pressure in a station side of a piping at time t0, a step for starting the supply of hydrogen gas from the station at time t1 that is after the pre-supply upstream pressure is acquired, a step for acquiring a post-supply upstream pressure at time t2 that is immediate after the supply of hydrogen gas starts, a step for acquiring a start-time flowrate that is a flowrate of hydrogen gas at the same period as the step for starting, a step for estimating the pressure loss generated in the piping at the time of the supply by using the pre-supply upstream pressure, post-supply upstream pressure, and the start-time flowrate, and a step for stopping the supply of hydrogen gas so that a tank pressure conforms with a predetermined target pressure.