For quantitative assessments of the effect of artificial reefs to accumulate fish school. we developed a low cost fish school monitoring system (FISCHOM). which enables visual and acoustical observation of fish resources for more than several days. In this paper, we report the profile of prototype FISCHOM and the outcome of trial survey. FISHCOM is consisted of two sensors (a stereo camera with two strobe lights and an echo sounder), a programmable timer, a battery, and a pressure resistant housing with a visually and acoustically transparent window for the sensors. All components except for the housing were selected from inexpensive articles on the market. A digital camera captured two visual images apart 50 cm away each other, which was combined together by a stereo photogrammetric mirror. The stereo images enable us to measure the three-dimensional information of fish school (e.g. fish length tilt angle, distribution). Two sensors acquire a set of data every optional interval (from several seconds to hours) controlled by the programmable timer. A trial survey was carried out at a high-rise artificial reef located off Atsumi, Yamagata prefecture on May 2003. FISCHOM succeeded a 5 days monitoring with an hour interval of data acquisition. We obtained a time series data of individual number of fish, fish length and distance from FISHCOM by the stereo camera, and fish school distribution by the echo sounder. We have demonstrated that the FISCHOM is appropriate to obtain quantitative and continuous data of fish school than other observation methods, which commonly used for the artificial reef assessment, such as observation by SCUBA diver, angling sampling and fish echo sounder operated on a boat.