A method for detecting a fault in a leakage inspector (500, 510) that measures a change in air pressure inside a device in a state in which the air pressure inside the device is made higher than air pressure outside the device and checks whether or not the device has a leak according to the change in air pressure inside the device, characterized in that the method comprises a calibration step and an inspection step, the calibration step comprising: a step of applying pressure to an inside of a first device serving as a reference device; a step of sealing air inside the first device; a step of calculating a differential value BB1 of pressure inside the first device with respect to time, at a first point that is elapsed a first predetermined period of time from an end point of the step of sealing the air inside the first device, and of storing the differential value BB1 in a storage section; and a step of calculating a differential value BB2 of the pressure inside the first device with respect to time, at a second point that is elapsed a second predetermined period of time from the first point, and of storing the differential value BB2 in the storage section; and the inspection step comprising: a step of applying pressure to an inside of a second device to be checked for a leak; a step of sealing air inside the second device; a step of calculating a differential value BB1' of pressure inside the second device with respect to time, at a third point that is elapsed the first predetermined period of time from an end point of the step of sealing the air inside the second device, and of storing the differential value BB1' in the storage section; and a step of calculating a differential value BB2' of the pressure inside the second device with respect to time, at a fourth point that is further elapsed the second predetermined period of time from the third point, and of storing the differential value BB2' in the storage section; a step of calculating a waveform ratio K as (BB 1' - BB2')/(BB1 - BB2); and a step of deciding whether an operation malfunction occurs by using the value of the waveform ratio K. a step of applying pressure to an inside of a first device serving as a reference device; a step of sealing air inside the first device; a step of calculating a differential value BB1 of pressure inside the first device with respect to time, at a first point that is elapsed a first predetermined period of time from an end point of the step of sealing the air inside the first device, and of storing the differential value BB1 in a storage section; and a step of calculating a differential value BB2 of the pressure inside the first device with respect to time, at a second point that is elapsed a second predetermined period of time from the first point, and of storing the differential value BB2 in the storage section; and the inspection step comprising: a step of applying pressure to an inside of a second device to be checked for a leak; a step of sealing air inside the second device; a step of calculating a differential value BB1' of pressure inside the second device with respect to time, at a third point that is elapsed the first predetermined period of time from an end point of the step of sealing the air inside the second device, and of storing the differential value BB1' in the storage section; and a step of calculating a differential value BB2' of the pressure inside the second device with respect to time, at a fourth point that is further elapsed the second predetermined period of time from the third point, and of storing the differential value BB2' in the storage section; a step of calculating a waveform ratio K as (BB 1' - BB2')/(BB1 - BB2); and a step of deciding whether an operation malfunction occurs by using the value of the waveform ratio K. a step of applying pressure to an inside of a second device to be checked for a leak; a step of sealing air inside the second device; a step of calculating a differential value BB1' of pressure inside the second device with respect to time, at a third point that is elapsed the first predetermined period of time from an end point of the step of sealing the air inside the second device, and of storing the differential value BB1' in the storage section; and a step of calculating a differential value BB2' of the pressure inside the second device with respect to time, at a fourth point that is further elapsed the second predetermined period of time from the third point, and of storing the differential value BB2' in the storage section; a step of calculating a waveform ratio K as (BB 1' - BB2')/(BB1 - BB2); and a step of deciding whether an operation malfunction occurs by using the value of the waveform ratio K.