Disclosed is an active material that can reduce an interface resistance with a sulfide solid electrolyte and improve the battery performance. The active material exhibits at least one peak in the range of from 0.145 nm to 0.185 nm and at least one peak in the range of from 0.28 nm to 0.31 nm in a radial distribution function obtained through measurement of an X-ray absorption fine structure of the active material. The active material is for use in a solid-state battery. The active material preferably has a core particle, and a coating layer located on the surface of the core particle.