All-solid-state capacitor includes an inorganic solid electrolyte, and a pair of current collectors disposed so that the inorganic solid electrolyte is interposed therebetween. In the all-solid-state capacitor, the inorganic solid electrolyte has a polycrystalline structure composed of crystal particles and crystal grain boundaries formed between the crystal particles. In a first crystal particle included in the crystal particles, a domain located near the crystal grain boundaries is larger in size than a domain located near the center.