PURPOSE: To obtain a method and device for performing fatigue tests on car bodies by which fatigue tests can be directly performed on the whole body or part of a box car.

CONSTITUTION: After the whole body or part of a box car 12 having an airtight body structure 12' is put in an airtightly sealed tank 1, the pressure in the tank 1 is lowered from the atmospheric pressure and, at the same time, a gas pressure difference is generated between the pressure in the tank 1 and pressure in the car body 12 so that an internal can occur in the body structure 12' and the air is introduced into the tank 1. Fatigue tests are performed by the above- mentioned pressure variation by introducing air into the tank then generating the pressure difference.