A method for leak testing includes a leak testing step and a reference leak step. In the leak testing step, a hollow work 20 as a test object is encapsulated in a work capsule 11. A test pressure is supplied to the work capsule 11 through a path 2a connected to the work capsule. A variation of pressure inside the work capsule 11 is detected in a condition in which the path 2a is shut-off, and a judgment is made whether a leakage through the work is generated based on the detected output. In the reference leak step, a reference leak device 30 having a known pinhole 31a is mounted on a work 20′ for reference leakage that is same as the work 20 as the test object. The work 20′ for reference leakage is encapsulated in the work capsule 11. The test pressure is supplied to the work capsule 11 via the path 2a, and a reference leakage is generated in the work 20′ for reference leakage via the reference leak device 30 in a condition in which the path 2a is shut-off. A variation of pressure inside the work capsule 11 accompanying the reference leakage is detected.