1. An image processing device for detecting a human face from a subject image, the device comprising: an imaging unit that captures a subject image; and a detection unit that detects a face from the subject image and that has at least processing for detecting a relatively-large-size face as the face, which is performed first, and processing for detecting a relatively-small-size face as the face, which is performed after the processing for detecting the relatively large face size, wherein the detection unit first repeats, a plurality of times, processing for detecting the relatively-large-size face and outputting a detection result, before processing performs processing for detecting the relatively-small-size face and outputting a detection result; wherein the detection unit detects a face while masking predetermined areas on both lateral ends of the subject image, to thus eliminate the predetermined areas from a processing target, and a face is detected without performance of masking operation in any of the plurality of processing operations for detecting a large-size face.