There is provided with an enzyme electrode which can be used as a sensor with high sensitivity, a biofuel cell with high output, and an electrochemical reaction device with high reaction efficiency. The enzyme electrode has a conductive base plate, a fusion protein immobilized to the conductive base plate and an electron transfer mediator, wherein the fusion protein is a fusion protein of a enzyme 1 to catalyze a chemical reaction for producing a reaction product 1 from a reaction substrate 1 and a enzyme 2 to catalyze a chemical reaction for producing a reaction product 2 from a reaction substrate 2, and at least one chemical substance of the reaction product 1 is identical to at least one chemical substance of the reaction substrate 2.