To provide an underwater light in which a power supply switch can be operated easily, while securing high waterproofness.

The underwater light 100 comprises a body case 3 of nearly cylindrical shape; a battery case 5 of nearly cylindrical shape which is arranged coaxially at one end side of the body case 3 housing a battery 8 and is engaged with waterproof structure; a light source case 4 of nearly cylindrical shape which is arranged coaxially at the other end side of the body case 3, housing a light-emitting diode 7 and is engaged with waterproof structure; a circuit part 6 which is fitted inside the body case 3 and electrically connects the light-emitting diode 7 with the battery 8; and a slide switch 2 which is fitted inside the body case 3 and switches over electrical connecting state of the circuit part 6. The light source case 4 is turnably engaged with the body case 3 around its center axis, and a switch sliding member 1 which turns integrally with the light source case 4 in the body case 3 and makes slide the slide switch 2 is installed.