A porous carbon electrode substrate hardly causes a short circuit when used in a fuel cell, and from which carbon fibers protruding from the substrate surface, carbon fibers that protrude from the substrate surface when the porous carbon electrode substrate is pressurized in a direction perpendicular to a surface thereof, and short carbon fibers that are insufficiently bonded at the substrate surface have been sufficiently removed. The porous carbon electrode substrate includes short carbon fibers and carbonized resin bonding the short carbon fibers, the porous carbon electrode substrate having an average short circuit current value measured at a first surface of 10 mA or less.