A shift register memory of molecular photodiode, consisting of flavin/ viologen/TCNQ molecular hetero-LB film, at the molecular level is described. In the shift register memory device, the free electrons of sensitizer molecules have an excited or ground ("1" or "0") state and the electrons are shifted between the functional molecules with photoinduced electron transfer reactions. Based on the transient photocurrent measurement, the shift register memory functions of molecular photodiode were observed with nanosecond time resolution.