A solid electrolyte, in which a part of an element contained in a mobile ion-containing material is substituted, and an occupied impurity level that is occupied by electrons or an unoccupied impurity level that is not occupied by electrons is provided between a valence electron band and a conduction band of the mobile ion-containing material, and a smaller energy difference out of an energy difference between a highest level of energy in the occupied impurity level and an energy and a LUMO level difference between a lowest level of energy in the unoccupied impurity level and a HOMO level is greater than 0.3 eV.