A secondary battery includes a positive electrode, a first aqueous electrolyte held on the positive electrode, a negative electrode, a second aqueous electrolyte held on the negative electrode, and a separator interposed between the positive electrode and the negative electrode. A difference between an osmotic pressure (N/m2) of the first aqueous electrolyte and an osmotic pressure (N/m2) of the second aqueous electrolyte is 90% or less (including 0%) of the higher one of the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte.