1. A content retrieval apparatus, comprising: retrieval image input means which receives input of a plurality of retrieval images being still images; image feature quantity extracting means which extracts image feature quantity of each of the plurality of retrieval images with a predetermined method; similarity degree calculation means which calculates a similarity degree of content of a moving image between the image feature quantity previously extracted from a still image of a frame structuring the content and the image feature quantity of each of the retrieval images; specifying means which specifies a frame of the still image being similar to each of the retrieval images by comparing the calculated similarity degree with a predetermined threshold value; and timeline displaying means which generates display data for performing timeline displaying by displaying the content on a time axis along with information indicating a temporal position of the frame of the still image being similar to each of the retrieval images based on the specified frame and metadata which is previously extracted from the content, wherein the timeline displaying means generates display data for displaying a screen having a retrieval image display unit which displays a list of the plurality of retrieval images and a timeline display unit which displays the content on a timeline, the plurality of retrieval images are displayed at the retrieval image display unit while being surrounded respectively by display frames in mutually different colors, and information indicating a temporal position of the frame of the still image being similar to each of the retrieval images is displayed at the timeline display unit as a color bar in a same color as a color of the display frame.