PURPOSE: To simplify the structure by dividing a hose into a first hose which has been connected to a speed detector and a second hose which has been connected to a hydraulic pressure takeoff port (nipple) and extending the second hose along the side face of the upper casing.

CONSTITUTION: A second conducting path 62 extends through a pressure receiving hole 56 and a first conducting path 58 from a hydraulic pressure detecting port 48, to the diagonal upper part from the conducting path 58, and also, toward the front end of the lower casing 50, and terminal at nipple 64. The nipple 64 is the upper end part of the casing 50 and positioned in front of the front end of the upper casing 51, and to its end part, the second flexible hose 66 is connected. The hose 66 runs along the upper end face of the casing 50, and also, extends to the rear along the side face of the casing 51, and terminated at a rise part 68. To the rise part 68, the first hose 80 is connected through a one-touch coupler 76, and the hose 80 is connected to a speed detector 82 which has been placed in the ship. In such a way, it becomes unnecessary to allow the conducting path of hydraulic pressure to pass through the casing 51 of a complicated structure, and the connecting work for the hoses 66, 80 can be facilitated.