To provide a means capable of improving cycle durability of electric devices, such as a lithium ion secondary battery. The present invention uses a negative electrode active material for an electric device, said negative electrode active material being formed of a silicon-containing alloy having a predetermined composition. The present invention is characterized in that, in an X-ray diffraction measurement of the silicon-containing alloy, said X-ray diffraction measurement using a CuKalpha1 beam, a ratio value (B/A) of a diffraction peak intensity B of the (001) plane of Sn with respect to the diffraction peak intensity A of the (111) plane of Si is 0.3-3.7. The diffraction peak of the (111) plane of Si is within a range where 2theta=24-33DEG, and the diffraction peak of the (001) plane of Sn is within a range where 2theta=26-35DEG.