The invention provides an all-solid-state capacitor (1) including an inorganic solid electrolyte (2), and a pair of current collectors (3) disposed so that the inorganic solid electrolyte (2) is interposed therebetween. In the all-solid-state capacitor (1), the inorganic solid electrolyte has a polycrystalline structure composed of crystal particles (21) and crystal grain boundaries (22) formed between the crystal particles (21). In a first crystal particle (21D) included in the crystal particles (21), a domain (5B) located near the crystal grain boundaries (22) is larger in size than a domain (5A) located near the center.