A stern structure of a ship includes a plurality of propellers (10,22), a plurality of propeller shaft tubes (11,21) configured to be provided correspondingly to the plurality of propellers (10,22), and a plurality of propeller shafts (12,22) connected to the plurality of propellers (10,20) being inserted into the plurality of propeller shaft tubes (11,21). A stern structural body (6) is configured to be provided so as to be joined to a rear part of a stern body (3), and support portions of the plurality of propeller shafts tubes (11,21) extending backwardly from the stern body (3). The stern structural body (6) includes a side fin (63,73) configured to extend backwardly from the stern body (3), spread externally with respect to the ship body center line (C) and be joined to side portions of the plurality of propeller shaft tubes (11,21) to support the plurality of propeller shaft tubes (11,21), and an upper fin (62,72) configured to be provided separately at a rear of the stern body (3), extend downwardly from a bottom of the stern body (3) and be joined to upper portions of the plurality of propeller shaft tubes (11,21) to support the plurality of propeller shaft tubes (11,21). The side fin (63,73) and the upper fin (62,72) are joined to the stern body (3) to coincide with directions of stream lines around the ship body.