According to one embodiment, there is provided an active substance. The active substance includes secondary particles and a carbon material phase formed on at least a part of a surface of each of thesecondary particles. Each of the secondary particles is constructed by aggregated primary particles of an active material. The primary particles of the active material includes a niobium composite oxide represented by LixM<1-y>NbyNb2O<7+delta>, wherein M is at least one selected from the group consisting of Ti and Zr, and x, y, and delta respectively satisfy 0<=x<=6, 0<=y<=1, and -1<=delta<=1. Thesecondary particles have a compression fracture strength of 10 MPa or more.