1. A medical diagnosis apparatus configured to obtain a signal for generating an image of an observation target and configured to cause an external display device to display an observation image based on the obtained signal to perform diagnosis, the medical diagnosis apparatus comprising: a detection unit configured to detect a shape of a finger of a practitioner and a spatial position of the finger of the practitioner; an executable command selection unit configured to select one or more commands executable by the medical diagnosis apparatus in accordance with the shape and the spatial position of the finger of the practitioner detected by the detection unit; a command image generation unit configured to generate a command image corresponding to the one or more commands selected by the executable command selection unit and to generate a finger shape image indicating the shape of the finger of the practitioner; and a display image generation unit configured to generate a display image using the command image and the finger shape image, generated by the command image generation unit, and the observation image.