An immobilized enzyme electrode effective in measurement of the substrate concentration of the enzyme and in conversion from enzyme reaction energies into electric energies. The immobilized enzyme, of an oxidase system, such as glucose oxidase, amino acid oxidase, xanthine oxidase or the like and a metal oxide capable of constituting a redox system which is reduced through coupling with these enzyme reactions and is electrochemically oxidized (anodic oxidation) are combined with each other. The use of the enzyme electrode allows the determination quantity of the enzyme substrate as extremely low as approximately 10.sup.-5 to 10.sup.-6 mole/l in concentration.