1. A display control device which displays images used for retrieving a piece of content data from among a plurality of pieces of content data displayed on a display unit, the display control device comprising: a retrieval image generation unit configured to generate images which are used in a retrieval operation and which include retrieval condition images and item images each arranged on a plane by arranging the retrieval condition images, which indicate a plurality of retrieval conditions for the plurality of pieces of content data, in a first direction on the plane, and by arranging, in a second direction on the plane, the item images which indicate pieces of content data or folders including pieces of content data categorized based on the retrieval conditions represented by the retrieval condition images arranged in the first direction; and a retrieval image display control unit configured to display on the display unit the images used in the retrieval operation generated using the retrieval image generation unit, to detect an operation input, and to move an indicator, which is used for indicating a selected one of the retrieval condition images and the item images, in a vertical direction or in a horizontal direction in accordance with the detected operation input, wherein the selected one of the item images is a folder representing a first layer of information, and in response to the retrieval image display control unit detecting operation input that requests expansion of the folder, further item images associated with the folder are also displayed in the plane and are arranged, together with the selected one of the retrieval condition images and the selected one of the item images, along a same line in the second direction, the further item images representing a second layer of information, and the item images are folders representing associated first layers of information, and in response to the retrieval image display control unit detecting operation input that requests expansion of the folder associated with the selected one of the item images, the retrieval condition image that represents the retrieval condition that categorizes the selected one of the item images is expanded along the first direction, each of the item images that are categorized based on the retrieval conditions represented by that retrieval condition image are arranged along the first direction at a same distance in the second direction from the expanded retrieval condition image, and further item images associated with the folders of the item images arranged along the first direction are also displayed in the plane and are arranged along a same line in the second direction as the item image associated with that further item image, the further item images representing the second layer of information.