As a method of sending electric power to underwater vehicles, the contactless power supply system (CLPS) utilizing electro magnetic induction is proposed. And we developed the cone-type coil that is suitable for use underwater. This system has efficient nature and high power transmission capability, even when the fluctuation in the sea exists. Furthermore, the electromagnetic force generated during power transmission will be useful for maintaining the location of an underwater vehicle stably. If this system is applied to the vehicle, the restriction of a sphere of activity and time in inquiry is go out. So it is possible to reduce in costs. In this paper, we considered about water-cooled and it is confirmed possible to transmit about 1[kW] of electric power at about 90 [%] of efficiency when the diameter of the coil is 48[mm]. And we designed the coil size which is suitable for the specification of battery on the real vehicle.