1. An image search apparatus for searching for an image, comprising: an obtaining unit configured to perform an obtaining process of obtaining, from a search key image set out of a plurality of images to generate a search condition, at least either of feature amounts of the search key image and image capturing conditions of the search key image; a generation unit configured to perform a generation process of generating a plurality of search conditions different from each other from the at least either of the feature amounts and the image capturing conditions obtained by said obtaining unit; a search unit configured to perform a search process of searching the plurality of images except the search key image for an image matching or similar to the search condition for each of the plurality of search conditions generated by said generation unit; a display control unit configured to perform a display control process of controlling a display unit to display a plurality of images that are images found for the plurality of search conditions by said search unit; a selection unit configured to perform a selection process of selecting, in accordance with a user operation, one image from the plurality of images displayed on the display unit by said display control unit; a setting unit configured to perform a setting process of setting, as a new search key image, the image selected by said selection unit; and a control unit configured to, when said setting unit sets the new search key image, control said obtaining unit, said generation unit, said search unit, said display control unit, said selection unit, and said setting unit to perform the obtaining process, the generation process, the search process, the display control process, the selection process, and the setting process using the new search key image.