The invention provides an electrolytic solution for an aluminum electrolyte capacitor with which there is little deterioration of the electrolytic solution properties, the sparking voltage is high, and shorting does not occur, even when the voltage used is high. The invention also provides an electrolyte (C) formed from anions of at least one phosphoric acid alkyl ester (A) and amidinium cations (B), at least one boric acid compound (F) selected from the group consisting of boric acid and boric acid esters, a C2-15 carboxylic acid (D) formed from carbon atoms, oxygen atoms, and hydrogen atoms only, and an organic solvent (E).