PURPOSE: To provide a rust preventive device for a valve of a four cycle engine in a small-sized marine vessel which improves durability and reliability of the four cycle engine by preventing rust generation of a shaft of a valve arranged in the four cycle engine while securing operation performance of the valve.

CONSTITUTION: An oil charging port is formed on an upper portion of a choke valve 3 for charging oil to valve shafts 1a, 2a, 3a, 9a of an intake valve 1, a throttle valve 2, the choke valve 3 and an intake valve 9 arranged on a four cycle engine in a small-sized marine vessel 12. An electromagnetic pump 6 is arranged at the oil charging port for introducing oil from an oil tank to the oil charging port. A maintenance switch 7 is connected to the electromagnetic pump 6 for operating it.