To provide a differential pressure type flow rate measurement method and a device capable of obtaining correct reference pressure and achieving precise measurement by preventing an influence by heat generated during the discharging operation of measured side work.

In order to compare a reference value with pressure at the time of injecting a fluid within a measured side pressure storage tank 1S having a discharge pipe 4S equipped with an orifice, a reference side pressure storage tank 1M and an injector 3M are disposed in parallel with the measured side pressure storage tank 1S and an injector 3S. The reference side pressure storage tank 1M and the injector 3M have specifications the same as those of the measured side pressure storage tank 1S and the injector 3S. A discharge pipe 4M extending from the reference side pressure storage tank 1M is closed when injecting the fluid by the injector, and the flow rate of the fluid is measured based on a pressure difference between the reference side and measured side tanks 1M and 1S. Since reference side and measured side circumstances can be made the same, conditions of the reference side pressure storage tank 1M when injecting the fluid into the tank by the injector can be also the same as those of the measured side pressure storage tank 1S. Therefore, it is possible to obtain proper reference pressure in the reference side pressure storage tank 1M, and differential pressure between the reference pressure and the pressure measured on the measured side can be obtained precisely so that the measurement accuracy is improved.