Provided is a leak testing method of a workpiece including spaces which are three partitioned void portions, the leak testing method being capable of separately learning an amount of leakage from each of the spaces, and precisely determining whether the workpiece is normal or defective. The leak testing method includes steps of obtaining total leakage amounts, and a step of calculating, based on the obtained total leakage amounts, a first leakage amount, a second leakage amount, a third leakage amount, a fourth leakage amount, a fifth leakage amount and a sixth leakage amount which are amounts of leakage from respective routes when gas is injected to a workpiece at a predetermined pressure.