An embodiment of the present invention provides a flexible all-solid-state battery including a weight energy density comparable to that of a conventional lithium-ion battery using an electrolytic solution and having a high level of safety that does not short-circuit even when bent under an excessive bending load. According to an embodiment of the present invention, a flexible all-solid-state battery including a layer of a solid-state polymer electrolyte arranged between a layer of a separator supporting the solid-state polymer electrolyte and a layer including a negative electrode active material is provided. In the flexible all-solid-state battery, the separator may include a woven fabric, a knit, or a non-woven cloth of an inorganic fiber or a polymeric fiber of 1 g/m2 to 70 g/m2 with a thickness in a range from 1 µm to 100 µm, an oxide ceramic particle layer including oxide ceramic particles with a particle size from 1 µm to 20 µm at a filling rate in a range from 5% to 60%, or a complex of the woven fabric, the knit, or the non-woven cloth and the oxide ceramic particles.