1. An image processing apparatus comprising: a partial image region setting unit for obtaining a picked-up image at a first time point as a standard image from time-series picked-up image data obtained by an image pickup unit picking up a detection subject and selecting a plurality of partial image regions including an image region of the detection subject in the standard image and a movement detection unit for obtaining a picked-up image at a second time point that is different from the first time point as a reference image and detecting a movement of the detection subject between the standard image and the reference image based on a difference between a state of pixel values of the partial image regions of the standard image and a state of pixel values of partial image regions of the reference image, wherein the partial image region setting unit sets a standard point used as a standard for relative positions of the partial image regions; and the movement detection unit obtains the state of the pixel values of the partial image regions of the reference image with the relative positions of the partial image regions with respect to the standard point being unchanged and calculates the difference between the obtained state of the pixel values of the partial image regions and the state of the pixel values of the partial image regions of the standard image to calculate a position of the standard point in the reference image.