A bioelectronic device consisting of protein-adsorbed hetero-Langmuir-Blodgett (LB) films was investigated. Four kinds of functional molecules, cytochrome c, viologen, flavin, and ferrocene, were used as a secondary electron acceptor (A2), a first electron acceptor (A1), a sensitizer (S), and an electron donor (D), respectively. To fabricate the cytochrome c adsorbed hetero-LB film, poly-L-aspartic acid was used as the bridging molecule. The hetero-LB film was fabricated by subsequently depositing ferrocene, flavin, and viologen onto the pretreated ITO glass. Cytochrome c-adsorbed hetero-LB films were prepared by the adsorption of cytochrome c onto the poly-L-aspartic acid treated-LB films by intermolecular electrostatic attraction. Finally, the MIM (metal/insulator/metal) structured molecular device was constructed by depositing aluminum onto the surface of the cytochrome c-adsorbed hetero-LB films. Hetero-LB films were analyzed by Atomic Force Microscopy (AFM), and cytochrome c adsorption onto the films confirmed. The photoswitching function was achieved and the photoinduced unidirectional flow was in accordance with the rectifying characteristics of the molecular device. The direction of energy flow was in accordance with the energy level profile across molecular films. Based on the measurement of the transient photocurrent of the molecular device efficient directional flow of photocurrent through the redox potential difference was observed. The photodiode characteristics of the proposed bio-electronic device were verified and the proposed molecular array mimicking the photosynthetic reaction center could be usefully applied as a model system for the development of the bio-molecular photodiode.