A propeller 10 setting a small duct 20 of the present invention includes a propeller 10 and a duct 20. A diameter Ddin of the duct is set to 20% or more and 50% or less of a diameter Dp of the propeller 10, and a pitch H of the propeller 10 is a decreasing pitch which reduces in a radial direction of the propeller 10, and which becomes a maximum value at a blade root of the propeller 10 and becomes a minimum value at a blade tip of the propeller 10. The small duct 20 is placed in front of and close to the propeller 10. According to this, in an actual sea, cavitation is suppressed, and a load distribution of the propeller 10 in its radial direction which governs efficiency is optimized by utilizing interference with respect to the small duct 20.