1. A non-invasive living body measuring device for measuring components contained in a blood, comprising: a device body; and a mounting part that is configured to be movably mountable on a wrist of a living body and holds the device body, wherein the device body comprises: an imaging part including a lens and an image pickup element, and configured to image the wrist of the living body by the image pickup element through the lens; a display part; and a controller that displays an image of the wrist obtained by the imaging part on the display part, generates a blood vessel image showing a blood vessel within the obtained image of the wrist, and displays the generated blood vessel image and two index lines on the display part, a region between the two index lines representing a suitable region for imaging a blood vessel by the imaging part, wherein the mounting part holds the device body so as to be rotatable around an optical axis of the lens, and wherein the controller measures the components in a blood by analyzing a blood vessel image of the wrist obtained by the imaging part.