To further accurately reflect force acting on a hull from a stern duct of an actual ship in a test of using a stern duct model.

Both left and right end parts of the stern duct model 4 arranged in front of a propeller 3 are installed in both side parts of a bossing part 5 of a stern part 2 of a model ship 1 via a duct stay model 12 and a measuring structure 13. The measuring structure 13 has a columnar part 14 already known to be a correlation between force acting in the longitudinal and vertical direction and the twisting direction and a stain quantity of bending strain and twisting strain in the longitudinal and vertical direction as a columnar shape of extending in the lateral direction, and comprises a strain gauge for measuring the bending strain and the twisting strain in its longitudinal and vertical direction. The longitudinal and vertical direction and moment force actually transmitted to the bossing part 5 side of the hull via the duct stay model 12 when fluid force is generated in the stern duct model 4, are derived based on the strain quantity of the bending strain and the twisting strain in the longitudinal and vertical direction generated in the columnar part 14 of the measuring structure 13.