The movement of the trolling depressor is important for catching the target species. The purpose of this study is to clarify the dynamics of the trolling depressor by using the data-logger. A fiume tank experiment was conducted to measure the tension of the line and the attitude and the angular velocities of the trolling depressor. The length of the main line was 2.5m. The flow speed was 1.10m/s. In this experiment, a two times larger model of the trolling depressor was used to install the underwater motion measuring unit. The acceleration, the attitude and angular velocities of the trolling depressor were measured by using this unit at the intervals of 0.01 seconds. As a result of the experiment, it was possible to clarify the change of pitching angle, rolling angle, yawing angle of the trolling depressor, and each periods were 0.7, 1.4, 1.4 seconds.
