A multiple electrode includes a plurality of micro-electrodes provided on a substrate, and a wiring portion for providing an electrical signal to the micro-electrodes or extracting an electrical signal from the micro-electrodes. Each micro-electrode has porous conductive material on its surface, and the impedance of the micro-electrode is 50 kΩ or less. Preferably, the porous conductive material is gold, and formed by the passage of current at a current density of 1.0 to 5.0 A/dm2 for 10 to 360 sec. The multiple electrode may include micro-electrodes provided on a substrate in the form of a matrix, a lead line connected to the micro-electrodes, and an electrical junction connected to an end of the lead line.