A cocking loosening feedback method includes sensing sequential three-dimensional direction information of a golf club and three-dimensional direction information of the arm a user, analyzing the change of an angle between both three-dimensional information with respect to time, generating a cocking loosening evaluation variable based on the difference between the cocking loosening point and the impact point and the difference between the backswing top point and the impact point in the analyzed three-dimensional information, analyzing the evaluation variable based on a predetermined criterion to evaluate the cocking loosening, and providing its feedback information to the user.