A method of producing a carbon material which is mainly composed of graphene-containing carbon particles is provided. The method includes a step of producing carbon particles from an organic material by maintaining a mixture containing the organic substance as a starting material, hydrogen peroxide and water under conditions of a temperature of 300° C. to 1000° C. and a pressure of 22 MPa or more. The method further includes a step of heat-treating the carbon particles at a higher temperature than the temperature maintained in the carbon particle producing step. The carbon material produced by the present method has a structure in which substances such as ions can easily enter and leave the graphene structures of the carbon particles, making the carbon material be useful as active materials of secondary batteries and electric double layer capacitors.