Abstract: An active material of the present invention has fine pores formed in the interlayer of a carbon material capable of exhibiting electrochemical double layer capacitance. The fine pores are formed by forming an oxidized graphite structure combined with oxygen in the interlayer of a part or whole of the carbon material containing soft carbon and then removing a part or whole of oxygen in the interlayer. A method for producing an energy storage active material for use in an electrochemical double layer capacitor comprises pre-treating a carbon material through heat treatment and oxidizing the pre-treated carbon material using an oxidant. The method further comprises reducing the oxidized carbon material through heat treatment. The interlayer distances of an active material for respective steps, measured by a powder X-ray diffraction method, are 0.33˜0.36 nm in the pre-treatment step, 0.5˜2.1 nm in the oxidation step, and 0.34˜0.5 nm in the reduction step.