1. An apparatus for detecting a blinking state, the apparatus comprising: a state-of-eye distinguishing means for calculating a feature value that represents a state of an eye, for an eye-area which has been detected by searching a frame image, based on pixel data of pixels that constitute the eye-area; a threshold value setting means for calculating a first threshold value representing the feature value at a first transition point from an open state to a closed state and a second threshold value representing the feature value at a second transition point from the closed state to the open state, based on the feature value calculated for a targeted eye when the targeted eye is open, and storing the calculated first threshold value and the calculated second threshold value in a memory; and a blinking state detection means for detecting the blinking state of the eye corresponding to the eye-area, by sequentially comparing the feature values, which are sequentially calculated for a series of the frame images by the state-of-eye distinguishing means, with one of the first threshold value and the second threshold value, which have been stored in the memory by the threshold value setting means.