According to one embodiment, an active material is provided. The active material includes an Nb2TiO7 phase and at least one Nb-rich phase selected from the group consisting of an Nb10Ti2O29 phase, an Nb14TiO37 phase, and an Nb24TiO64 phase. The active material includes potassium and phosphorus, and a total concentration of potassium and phosphorus in the active material is in the range of 0.01% by mass to 5.00% by mass. An average crystallite diameter is in the range of 80 nm to 150 nm. In a particle size distribution chart obtained by a laser diffraction scattering method, D10 is 0.3 μm or greater, and D90 is 10 μm or less. The active material satisfies a peak intensity ratio represented by the following Formula (1).

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