A method of assembling a carriage assembly is capable of suppressing deformation of spacer portions when suspensions are attached to carriage arms. The method of assembling a carriage assembly aligns fitting holes provided in front end portions of carriage arms and spacer holes provided in spacer portions of suspensions and places the suspensions onto the carriage arms, and then presses a ball with a diameter equal to or greater than an inner diameter of the spacer holes with a pressure-applying member to pass the ball through the spacer holes, thereby crimping spacer hole edge portions of the spacer portions and attaching the suspensions to the front end portions of the carriage arms. By applying ultrasonic vibration from two axial directions to the pressure-applying member, the pressure-applying member is caused to vibrate on a two-dimensional movement path on a predetermined plane and passes the ball through the spacer holes while causing the ball to rotate.