There is provided a method of assembling a carriage assembly that can crimp suspensions to carriage arms by applying ultrasonic vibration to a crimping tool without causing deformation of the suspensions and the like. The method of assembling a carriage assembly aligns attachment holes provided in front ends of carriage arms and crimping portions provided on suspensions to set the suspensions on the carriage arms and then presses a metal ball through crimping holes provided in the crimping portions while applying ultrasonic vibration to a crimping tool to crimp the suspensions to the carriage arms. The suspensions are crimped to the carriage arms by detecting stress that acts on the crimping tool when the metal ball is pressed in by the crimping tool and controlling the amplitude of the ultrasonic vibration applied to the crimping tool so as to increase and decrease in accordance with the magnitude of the stress.