The purpose of the present disclosure is to set the initial information of the anchoring object (target) of a ship with high accuracy. A ship navigation assistance system according to the present disclosure includes a provisional initial information specifier, a measurement sensor and processing circuitry. The provisional initial information specifier may accept a specification of provisional initial information for characteristic information on an object to which a ship anchors or docks (docks to a pier). The measurement sensor may acquire measurement information on an object using a ranging result of an area including the object.