An electrode active material comprising a silicon-containing carbon-based composite material obtained by: preparing a cured product of (A) a silicon-free organic compound having a crosslinkable group, and (B) a silicon-containing compound capable of crosslinking the component (A); and baking the cured product in an inert gas or in a vacuum at 300 to 1,500° C.; an electrode comprising the electrode active material; and an electricity storage device comprising the electrode. The electrode active material has high reversible capacity and stable charge and discharge cycle characteristics, has little electrical potential loss when lithium is discharged, and furthermore, can be manufactured via a simple manufacturing process. Therefore, an electrode active material that is particularly suitable for an electrode of a lithium secondary battery can be provided, and an electricity storage device having an electrode comprising the electrode active material can also be provided.