A varistor includes an effective layer having first and second surfaces opposite to each other, a first ineffective layer stacked on the first surface of the effective layer, a second ineffective layer stacked on the second surface of the effective layer, and an external electrode. The effective layer includes a ceramic layer having a polycrystalline structure including crystal particles exhibiting voltage nonlinear characteristics, and internal electrodes stacked alternately on the ceramic layer. The thickness of the second ineffective layer is equal to or more than 1.1 times a thickness of the first ineffective layer and equal to or smaller than 6 times the thickness of the first ineffective layer. This varistor has a small size and excellent surge resistance.