According to a first embodiment, there is provided a positive electrode including a positive electrode active material-containing layer containing a first active material having a spinel type crystal structure. The positive electrode satisfies the formulas (1) to (3) when combined with a negative electrode including a negative electrode active material-containing layer containing a first active material having a spinel type crystal structure: 0.5≤a1/b1≤1.5 (1); 0.4≤a2/b2≤1.4 (2); and 0.5≤a3/b3≤2.3 (3), where a1 and b1 are a pore volume per 1 g weight, a2 and b2 are a pore specific surface area, and a3 and b3 are a median diameter in pore distribution, for the positive and negative electrode active material-containing layers, respectively.