Research on an underwater exploration robot is gathering attention for developing marine resources and inspecting underwater structures. Robots that imitate living things can be used for exploration without affecting aquatic organisms. So far, an underwater robot has been developed using a propulsive mechanism with artificial pectoral fins, in which they were made by mimicking actual Manta's pectoral fins. In this robot, self-positional information is acquired by a method of estimating the self-position via optical flows. Note however that the depth distance from the body to the ground is required for estimating the self-position through optical flows. In conventional research, a range-finding system using multiple lasers was proposed to measure the distance, but the value calculated by the method was greatly variated due to the pitch motion characterized by a Manta-type robot. In this research, it is aimed at reducing the influence from pitch motion by introducing a gimbal mechanism. In this paper, it first describes the outline of the underwater robot to be used, the range-finding system using laser points, and the method for obtaining the distance to an object to be measured. Then, a range-finding method with multiple lasers is proposed and the effectiveness of the proposed method is verified by conducting some experiments on measuring the distance and calculating the angle.