1. A crack-propagation prediction method comprising: a correlation-information preparing step of measuring the length of a crack initiated in a test object by a plurality of inspectors and/or a plurality of inspection methods and obtaining correlation information between data acquired through the measurement and the condition of an actual crack; a crack-length estimating step of estimating the actual length of a crack initiated in an inspection target on the basis of the crack length measured by an inspector during inspection of the inspection target and the correlation information; and a crack-propagation-curve estimating step of estimating a crack-propagation curve of the inspection target originating from the crack length estimated in the crack-length estimating step.