A negative electrode active material which contains composite particles, each of which is composed of: nano-silicon aggregated particles produced by heat-treating a layered polysilane represented by composition formula (SiH)n and having a structure wherein a plurality of six-membered rings configured of silicon atoms are connected; and a carbon layer that is composed of amorphous carbon and is complexed by covering at least a part of the aggregated particles. The D50 average particle diameter of the aggregated particles is within the range of 0.2-30 [mu]m, and the D50 average particle diameter of the composite particles is within the range of 0.5-40 [mu]m.