The present invention relates to a silicon-based active material-polymer composite, which is a secondary particle formed by uniformly mixing a silicon-based particle, which is a primary particle, and a conductive polymer particle having a volume elastic modulus of 10 to 100 Pa at a temperature of 20 to 40C. The pulverization of the silicon-based particle is suppressed by a buffering action on stress generated by a volume change of the silicon-based particle, and the low electrical conductivity of the silicon-based particle can be complemented.