An electroconductive rubber roller (10) whose outermost layer consists of a rubber layer (1) made of a rubber composition containing an ionic-conductive rubber as a main component thereof. The surface of the rubber layer consists of an oxide film; and the rubber composition contains a dielectric loss tangent-adjusting filler to set a dielectric loss tangent of the electroconductive rubber roller to 0.1 to 1.5. Weak electroconductive carbon black and/or calcium carbonate treated with fatty acid can be used as the dielectric loss tangent-adjusting filler.