To provide a marine-gear apparatus which transmits a rotational power from a main engine mounted in a ship to a propeller, reduces an operation force necessary for manually operating a forward/backward operation tool for switching a forward/backward switching mechanism, and satisfies fail-safe issues.

A marine-gear apparatus 21 includes: an input shaft 23 to which a rotational power from a main engine 20 is inputted; a forward/backward switching mechanism for switching the rotational power of the input shaft 23 to an output for one of a forward moving, a neutral, and a reverse rotation; an actuation body 46 which switches the forward/backward switching mechanism into one of a forward moving state, a neutral state, and a backward moving state by a rotation movement; and an electrically-drive type actuator 50 which rotates the actuation body 46 in association with an operation of a forward/backward operation tool. The actuation body 46 includes a self-return member 56 which compulsory rotates the actuation body 46 to return the forward/backward switching mechanism to the neutral state when an electric power is not supplied to the electrically-drive type actuator 50.