The present study examines the relationship between the cell growth rate and luminescence intensity by fabricating a system that enables the simultaneous measurement of the luminescence intensity and optical density of the liquid culture of Photobacterium kishitani, in order to investigate a possible mechanism for the luminescence oscillation. An instrument is fabricated using a microcomputer-controlled LED and a photo IC diode for the measurements. Two signals, cell density and bacterial bioluminescence were distinguished from one data set. A possible hypothesis for the oscillation in bacterial bioluminescence from oxygen level viewpoint has been created.