A gas flow rate estimation device includes a first calculation unit that calculates, by using an average movement vector of a gas region included in an image, a gas passage time for leaked gas to pass through the gas region, a second calculation unit that calculates a gas volume in the gas region by using a gas concentration thickness product of the gas region, and a third calculation unit that calculates an estimated value of a flow rate of the gas by using the gas passage time and the gas volume.