NOVELTY - A new ionic liquid contains an oxazolinium or thiazolinium moiety (1), substituted at the 2-position by an oxygen- or sulfur-bonded moiety as cation component.    USE - Used as electrolyte liquid and reaction solvent for electrical storage device such as lithium secondary battery, electrical double layer capacitor, dye-sensitized solar cell and fuel cell (all claimed).    ADVANTAGE - The ionic liquid has favorable electrical conductivity and stability.    DETAILED DESCRIPTION - An ionic liquid contains an organic substance of formula (1) as cation component.    R1-R6=H, 1-30C linear or side chain alkyl, 2-30C linear or side chain alkenyl with one or more double bonds, 2-30C linear or side chain with one or more triple bonds, (un)saturated cycloalkyl, aryl, alkoxy alkyl or heterocyclic, where hydrogen atom contained in the substituents (R1-R6) is substituted partly or completely with halogen atom, or is substituted partly with CN group and NO2 group, and carbon atom contained in the substituents (R1-R6) is substituted with -O-, -C(O)-, -C(O)O-, -S-, -S(O)-,-SO2-, -SO3-, -N=, -N=N-, -NH-, -NR'-, -N(R')2, -PR', -P(O)R'-, -P(O)R'-O-, -O-P(O)R'-O- or P(R')2=N-;    R'=1-10C linear or side chain alkyl, alkyl substituted partly or completely with fluorine atom, (un)saturated cycloalkyl, (un)substituted phenyl or (un)substituted heterocyclic;    X,Y=sulfur or oxygen atom;and    dotted line=conjugation structure.    R3-R6 are optionally combined with C1 and/or C2 atoms, to form cyclic structure, aromatic ring structure or heterocyclic structure. R2 and R3 are optionally combined with C1 and/or N atom, to form cyclic structure, aromatic ring structure of heterocyclic structure.    INDEPENDENT CLAIMS are included for the following:    (1) electrical storage device;    (2) lithium secondary battery;    (3) electrical double layer capacitor;    (4) dye-sensitized solar cell;    (5) fuel cell;    (6) reaction solvent; and    (7) manufacture of ionic liquid, which involves alkylating organic substance of formula (2 or 3).    R1-R6,X,Y=defined above