To reduce wave resistance during full load and during light load with an easy design without increasing factors deteriorating propulsion performance of a hull.

In a bulbous bow device 2' including a bulb 21' protruded spherically to the front of the hull 1 at a bow 11 of the hull 1 in a ship, the bulb 21' is divided with respect to the hull 1. A basal end 21a' facing the hull 1 is formed in a vertical symmetrical shape and is arranged connectably to the hull 1 by a vertical rotation of 180 degrees. Further, when rotated 180 degrees, the bulb is formed so that the position of a front end 21b' is drifted vertically without protruding downward from a bottom 12 of the ship 1, in a first form that the front end 21' protruding most forwardly of the hull 1 is disposed more above than the center of the bulb, and in a second form that the front end 21' is disposed below the center thereof.