Energy storage device

An energy storage device according to an aspect of the present invention includes: an electrode assembly in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween; an electrolyte solution; and a sealable case for housing the electrode assembly and the electrolyte solution, in which a compressive modulus of elasticity of the separator is 15 MPa or more and an inside of the case is in a negative pressure state.