NOVELTY - A nonaqueous electrolyte comprises organophosphorus compound (I). The electrolytic salt of nonaqueous electrolyte is dissolved in nonaqueous solvent.    USE - Nonaqueous electrolyte is used for electrical storage device (claimed) e.g. lithium secondary battery used as power supply for mobile telephone, notebook computer and motor vehicle.    ADVANTAGE - The electrical storage device formed using the nonaqueous electrolyte has excellent electrochemical characteristics under high temperature, and cyclic characteristics.    DETAILED DESCRIPTION - A nonaqueous electrolyte comprises organophosphorus compound of formula: (P(=O)(-R1)(-R2)-(C(-R3)(-R4))m-(O)n-C(=O))q-X (I). The electrolytic salt of nonaqueous electrolyte is dissolved in nonaqueous solvent.    R1,R2=1-6C alkyl, 3-6C cycloalkyl, 2-6C alkenyl, 3-6C alkynyl, 1-6C alkoxy, 3-6C cycloalkoxy, 2-6C alkenyloxy, 3-6C alkynyloxy, 1-6C halogenoalkyl, 1-6C halogenoalkoxy, 6-12C aryl in which at least one H is optionally substituted by halo, or 6-12C aryloxy in which at least one H is optionally substituted by halo;    R1+R2=ring structure;    R3,R4=H, halo, or 1-4C alkyl;    m=1-4;    n=0 or 1;    q=1 or 2;    X=1-6C alkoxy, 3-6C alkynyloxy, 2-6C alkyloxy alkoxy, 6-12C aryloxy in which at least one H is optionally substituted by halo, -O-L1-OC(=O)-C(=O)-OR5, -O-L2-C(=O)-OR5, or -O-L5-CN (when q is 1, then n is 0), 1-6C alkyl, 2-6C alkynyl, 1-6C alkoxy, 3-6C alkynyloxy, 2-6C alkyloxy alkoxy or -C(=O)-OR5 (when q is 1, then n is 0), or -O-L3-O-, -OC(=O)-C(=O)O- or single bond (when q is 2);    R5=1-6C alkyl;    L1,L3=2-6C alkylene or 4-8C alkynylene;and    L2,L5=1-6C alkylene.    INDEPENDENT CLAIMS are included for the following:    (1) electrical storage device, which is provided with nonaqueous electrolyte in which electrolytic salt is dissolved in positive electrode, negative electrode, and nonaqueous solvent;    (2) additive, which contains organophosphorus compound; and    (3) organophosphorus compound of formula: (P(=O)(-R1)(-R2)-(C(-R3)(-R4))m-C(=O))q-X1.