Recently, many attempts have been made to use microalgae as raw material for next generation biodiesel. Since conventional microalgae detection is performed in the laboratory after collecting algae in the field, it is necessary to develop a portable fluorescence measuring device that can effectively reduce detection duration in the field. In this study, we developed a portable fluorescence measurement device composed of an optical system and a control system to detect microalgae in the field. The optical system stimulates excitation light suitable for algae to be measured and determines the amount of algae by measuring the amount of emitted light through the PMT sensor. The optical system facilitates seamless change of filters and lenses according to kinds of algae. This was validated by checking the amount of light measured according to concentration of CC125. Reliability of the fluorescence measuring device was verified through repeated experiments.