According to one embodiment, there is provided an active substance. The active substance contains active material particles. The active material particles comprise a compound represented by the formula: Ti1-xM1xNb2-yM2yO7. The active material particles has a peak A attributed to a (110) plane which appears at 2θ ranging from 23.74 to 24.14°, a peak B attributed to a (003) plane which appears at 2θ ranging from 25.81 to 26.21° and a peak C attributed to a (602) plane which appears at 2θ ranging from 26.14 to 26.54° in an X-ray diffraction pattern of the active material particles. An intensity IA of the peak A, an intensity IB of the peak B, and an intensity IC of the peak C satisfy the relation (1): 0.80≤IB/IA≤1.12; and the relation (2) IC/IB≤0.80.