To provide a simple and inexpensive navigation gate with improved safety and convenience for a worker by being unlocked only by the propulsion of a ship.

An inclinable lock pin 5 extended to a mating door body 3 to be engaged with and disengaged from a groove 3c of the door body 3 is mounted on one of two door bodies 3, 3 rotatable around a shaft. A press-up pin 5a as a press-up member, engaged with the lock pin 5 is vertically movably mounted just under the groove 3c. Slide arms 6 are longitudinally mounted on two door bodies 3, 3 slidably to each door body 3, 3. Ship protective members 7, 7 are mounted on front and rear ends of the slide arm 8. Further the slide arm 6 is provided with a buoy plate 8, and a compression spring 8a is mounted on the buoy plate 8. A V-shaped inclined face 8b is formed on an upper edge part of the buoy plate 8, and a lower end of the press-up pin 5a is engaged with the inclined face 8b.