The photoelectric responses of a biodevice consisting of chlorophyll $alpha$ Langmuir-Blodgett film were investigated. Chlorophyll $alpha$ Langmuir-Blodgett films were deposited onto ITO and Au coated glass. To confirm film formation, surface analysis of chlorophyll $alpha$ Langmuir-Blodgett film was carried out by measurement using atomic force microscopy. The metal/insulator/metal structured biodevice was constructed by depositing aluminum onto the chlorophyll $alpha$ Langmuir-Blodgett film surface. To investigate the photoelectric response, the current-voltage characteristic was measured by the conducting metal tip. The photoswitching function and transient photovoltage characteristics of the proposed device were measured by irradiation with Ar ion laser and $N_2$ pulse laser, respectively. This research suggested that the proposed biodevice consisting of chlorophyll $alpha$ could be applied to the molecular scale biosensor and/or bioelectronic device.