A swing diagnosing device utilizes a recording plate having an indicating surface fitted to the front surface of a supporting plate attached to a base plate, and a rotary ball is borne by a cover fixed to the base plate. A shaft pipe projecting out of an arm is passed through this rotary ball, a supporting metal piece fixing the grip end of a golf club is attached to the lower end part of the arm, and a recording means is fitted to the tip of the shaft pipe at the upper end so that as the arm is operatively rotated with the golf swing the locus of the swing is recorded.