An all-solid-state capacitor, comprising: an inorganic solid electrolyte; and a pair of current collectors (3A, 3B) formed on opposite surfaces of the inorganic solid electrolyte, the inorganic solid electrolyte having a polycrystalline structure, the all-solid-state capacitor satisfying a relationship given as: R1 < R2 < R3, a relationship given as: C1 < C3, and a relationship given as: C1 < C2, in which, R1, R2 and R3 are resistance components, and R1 denotes an intragrain resistance of the inorganic solid electrolyte, R2 denotes a grain-boundary resistance of the inorganic solid electrolyte and R3 denotes an interfacial resistance between the inorganic solid electrolyte and the current collector (3A, 3B), and, C1, C2 and C3 are capacitance components, and C1 denotes an intragrain capacity of the inorganic solid electrolyte, C2 denotes a grain-boundary capacity of the inorganic solid electrolyte and C3 denotes an interfacial capacity between the inorganic solid electrolyte and the current collector (3A, 3B), the all-solid-state capacitor being represented by an equivalent circuit formed of a first parallel circuit of the intragrain resistance R1 and the intragrain capacity C1, a second parallel circuit of the grain-boundary resistance R2 and the grain-boundary capacity C2 and a third parallel circuit of the interfacial resistance R3 and the interfacial capacity C3, the first parallel circuit, the second parallel circuit and the third parallel circuit being connected in series, characterized in that a value B which is expressed by the following formula falls in a range of 0.1 to 100 rad/s: B = 1 R 2 ⋅ C 2 an inorganic solid electrolyte; and a pair of current collectors (3A, 3B) formed on opposite surfaces of the inorganic solid electrolyte, the inorganic solid electrolyte having a polycrystalline structure, the all-solid-state capacitor satisfying a relationship given as: R1 < R2 < R3, a relationship given as: C1 < C3, and a relationship given as: C1 < C2, in which, R1, R2 and R3 are resistance components, and R1 denotes an intragrain resistance of the inorganic solid electrolyte, R2 denotes a grain-boundary resistance of the inorganic solid electrolyte and R3 denotes an interfacial resistance between the inorganic solid electrolyte and the current collector (3A, 3B), and, C1, C2 and C3 are capacitance components, and C1 denotes an intragrain capacity of the inorganic solid electrolyte, C2 denotes a grain-boundary capacity of the inorganic solid electrolyte and C3 denotes an interfacial capacity between the inorganic solid electrolyte and the current collector (3A, 3B), the all-solid-state capacitor being represented by an equivalent circuit formed of a first parallel circuit of the intragrain resistance R1 and the intragrain capacity C1, a second parallel circuit of the grain-boundary resistance R2 and the grain-boundary capacity C2 and a third parallel circuit of the interfacial resistance R3 and the interfacial capacity C3, the first parallel circuit, the second parallel circuit and the third parallel circuit being connected in series, characterized in that a value B which is expressed by the following formula falls in a range of 0.1 to 100 rad/s: B = 1 R 2 ⋅ C 2