1. A bead inspection method of inspecting quality of a bead that is formed by melting a brazing wire that is substantially continuously supplied to a joining portion between a plurality of metal workpieces so as to braze the metal workpieces to each other, comprising: forming a regression expression based on an actual measurement of a feature quantity that is information about a shape of a specific portion of the metal workpieces and the bead and that affects throat thickness of the bead, and on an actual measurement of the throat thickness corresponding to the actual measurement of the feature quantity; calculating a predicted value of the throat thickness by the regression expression; and determining whether or not the bead is good by comparing the predicted value of the throat thickness with a pre-set criterion value.