Provided are a nonaqueous solvent containing a compound with high conductivity and low viscosity and a high-performance power storage device using the nonaqueous solvent. The power storage device includes an ionic liquid. The ionic liquid contains an anion and a cation having a five-membered heteroaromatic ring having one or more substituents. At least one of the substituents is a straight chain formed of four or more atoms and includes one or more of C, O, Si, N, S, and P.