1. An imaging device, comprising: an image sensor which outputs a signal indicating a series of images obtained by sequential shooting; a tracking processing portion which, based on the output signal of the image sensor, detects a position of a tracking target on the series of images and thereby tracks the tracking target on the series of images; a tracking evaluation portion which, based on the output signal of the image sensor, evaluates a degree of reliability, or of ease, of tracking by the tracking processing portion, and classifies the degree into one of a plurality of levels; a display portion which displays the series of images; and a display control portion which makes the display portion display an evaluation result by the tracking evaluation portion.