In recent years, reducing carbon dioxide is being demanded in terms of preventing global warming. Lightening autobodies is one of the most practical ways to conduct it, for which converting the body sheets from conventional steel to Al-Mg-Si alloy is effective. Although the Al-Mg-Si alloys have the advantage that they have hardenability during paint baking and do not cause stretcher strain patterns, poor formability is a crucial drawback. Bendability is one of the most important properties related to formability. However, there has been no assessing method having both speediness and quantitative reproducibility. In this study, we have developed a assessing method based on the electric resistance decrease arising from the decrease in conducting section when cracks are formed by bending. Bendability was assessed by electrical resistance change as well as by crack density on the tension surface measured with an SEM. It was found that the new method have far greater speediness with the same quantitative reproducibility than the crack measurement method.