An enzyme electrode having an electroconductive base member, an oxidoreductase and an electron mediator has at least a portion (a) in which the oxidoreductase is immobilized on the electroconductive base member, and a portion (b) in which the electron mediator is immobilized on the electroconductive base member but the oxidoreductase is not immobilized on the electroconductive base member. A bio fuel cell having the enzyme electrode as at least one of an anode and a cathode allows optimization of a reaction condition of each one of a plurality of reaction steps, including an “enzymatic reaction”, an “electron transfer reaction”, etc. Thus, the bio fuel cell provides high output.