Trolling fishery is a typical fishing method used for catching fish that swim at high speeds, such as tuna, skipjack, and yellowtail, in tropical and subtropical regions. The structure of fishing gear is quite simple and consists of a rod, main line, trolling depressor, leader line and lure. The trolling depressor can be used to submerge the lure when it is being towed. The movement of the trolling depressor is important for catching the target species. The purpose of this study is to clarify the movement of a trolling depressor. The experiments were conducted using a flume tank to clarify the characteristic movement of the trolling depressor. A 3-component load cell measured the line tension. The displacement of the point where the line was connected to the trolling depressor was estimated by the line tension. The period of the y component's displacement was twice as long as those of the x and z component's displacement. It was clarified that the locus of the point was similar to number "8" on the xy, yz, and xz planes. A flume tank experiment was conducted to measure the tension of the line and the attitude and angular velocities of the trolling depressor. In this experiment, a 2 times larger model of the trolling depressor was used to install the underwater motion measuring unit. The acceleration, attitude and angular velocities of the trolling depressor were measured using this unit. This experiment enabled to clarify the change in pitching angle, rolling angle and yawing angle of the trolling depressor, and each period was 0.7, 1.4, and 1.4 seconds.