The invention provides a pressure measuring method and device that are capable of easily measuring the volume of a pipe that is an object of inspection and of eliminating the influences of a change in temperature in the pipe. A pressure measuring method using a pressure sensor 4 connected to a pipe for feeding a gas thorough a connecting portion for measuring the pressure in the pipe, the method being characterized in that the method comprises a pressurizing step for pressurizing the inside of the pipe by a pump 5 with the pipe held in the closed state, and a step for measuring an amount of pressure change of the pipe in the standing state after completion of the pressurization step, and in that an amount of pressurization change of the in-pipe pressure by the pressurization step, and the flow rate of the gas fed into the pipe during pressurization are measured, and the volume of the pipe in the closed state is calculated on the basis of the amount of pressurization change and the flow rate of the gas, and the amount of leakage of the gas from the pipe is calculated on the basis of the volume of the pipe and the amount of pressure change in the standing state.