The present invention provides: a nonaqueous electrolyte solution which is capable of improving electrochemical characteristics at high temperatures and is also capable of improving the capacity retention rate after a high temperature cycle test, while reducing the increase rate of electrode thickness; and an electricity storage device which uses this nonaqueous electrolyte solution. A nonaqueous electrolyte solution obtained by dissolving an electrolyte salt in a nonaqueous solvent, which contains 0.001-5% by mass of a diisocyanate compound represented by OCN-L-NCO (wherein L represents an alkylene group having 4-12 carbon atoms), and which additionally contains 0.001-5% by mass of at least one compound that is selected from among specific phosphoric acid ester compounds, specific cyclic sulfonic acid ester compounds, isocyanate compounds having specific ester structures, and specific triple bond-containing compounds; and an electricity storage device which uses this nonaqueous electrolyte solution.