Abstract: Embodiments of the present application provide a trackball apparatus, a medical input apparatus, and an ultrasonic imaging apparatus. The trackball apparatus includes a cover plate, a housing and a ball. The cover plate has a first surface and a second surface, where an opening portion passing through the first surface and the second surface is provided at the center of the cover plate, and one or more engaging portions are provided on the second surface. The housing has an accommodating portion, where when the cover plate is mounted on the housing, the one or more engaging portions are located on an outer side of the housing. The ball is accommodated in the accommodating portion in a freely rotatable state, where a part of the ball is exposed from the opening portion. In this way, the trackball apparatus can be easily mounted and detached, thereby facilitating maintenance and product replacement.