Coupling structure and coupling method for power transmission

A coupling structure for a power transmission comprising a propeller shaft, which transmits a rotational driving force, and a rotation-transmitting device, which is connected to said propeller shaft and transmits the rotational driving force, said coupling structure being for connecting said propeller shaft and said rotation-transmitting device;

• wherein:
• a first mark for indicating a direction of a rotational unbalance of said propeller shaft is provided on said propeller shaft while a second mark for indicating a direction of a rotational unbalance of a companion flange is provided on said companion flange, which is to be connected to said propeller shaft at said rotation-transmitting device;
• of the directions of said rotational unbalances indicated by said first mark and said second mark, one direction is set as a direction along which a rotating mass becomes larger while another is set as a direction along which a rotating mass becomes smaller;
• furthermore, one of said first mark and said second mark is provided over an angular region with a predetermined angle around an axis;
• and
• said propeller shaft and said companion flange are connected with each other on a basis of said first mark and said second mark,
• wherein said angular region is set approximately from +180/n to −180/n degrees, where n is a number of bolt holes used for connecting said propeller shaft and said companion flange.