NOVELTY - The apparatus has a storage tank (9) storing an electrolyte solution. A substrate holder (41) is mounted in the tank. A support unit (57) includes a set of support elements arranged in a direction of arrangement of substrates e.g. wafer, for contacting and supporting lower portions of circumferential surfaces of the substrates. A cover drive mechanism e.g. air cylinders, separates the support unit with another support unit when placing the substrates in the holder. The drive mechanism connects the support units after the substrates are placed in the holder.    USE - Anodizing apparatus for causing an anodizing reaction on substrates e.g. semiconductor wafer, in an electrolyte solution e.g. hydrofluoric acid, in an LCD, plasma display, organic electroluminescent device, field emission display, magnetic disk, magnetic optical disk, photomask, solar cell, and micro-electro-mechanical system (MEMS). Can also be used for an optical disk substrate.    ADVANTAGE - The support elements can support the lower portions of the circumferential surfaces, which correspond to chords shorter than diameters of the substrates, so as to allow the transport mechanism for transferring the substrates to and from the substrate holder to hold the substrates at portions below maximum diameter portions, so that the transport mechanism can hold the substrates reliably without applying stress to the substrates. The support units can be moved to positions to have inner surfaces turned upward when the support units are separated, so that bubbles generating from chemical reaction can be reduced. The apparatus can inhibit chemical reaction in the electrode tanks, so that degradation of electrodes can be inhibited, contamination of the substrates can be prevented, and operating rate of the apparatus can be improved.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of an anodizing apparatus.    Storage tank (9)    Inner tank (11)    Outer tanks (13)    Substrate holder (41)    Support unit (57)