1. A data management apparatus assigning metadata of a first kind and metadata of a second kind to a plurality of content data, the apparatus comprising: a display unit that displays the plurality of content data, according to a display mode selected from a plurality of display modes for displaying the plurality of content data, wherein the plurality of display modes includes a first display mode in which the plurality of content data is sorted and displayed based on an attribute information numeric value for specifying the metadata of the first kind and a second display mode in which the plurality of content data is sorted and displayed based on an attribute information numeric value for specifying the metadata of the second kind; and a processor configured to determine, when content data is selected from the plurality of content data displayed in the selected display mode, a candidate for metadata in accordance with an attribute information numeric value of the selected content data; and a metadata candidate display unit that displays the determined candidate for metadata, wherein metadata is assigned to the selected content data by an assignment unit, wherein the attribute information numeric value shows a month and a day in a case where the first display mode is a display mode for causing data to be displayed in date order, wherein the attribute information numeric value shows a latitude and a longitude in a case where the second display mode is a display mode for causing data to be displayed in position information order, wherein said processor determines, when the plurality of content data is displayed according to the first display mode and one of the plurality of content data being displayed according to the first display mode is selected as content data of interest, the candidate for metadata related to a date of the content data of interest as a display target, and determines, when the plurality of content data is displayed according to the second display mode and one of the plurality of content data being displayed according to the second display mode is selected as the content data of interest, the candidate for metadata related to position information of the content data of interest as a display target, and wherein said metadata candidate display unit displays, when one of the plurality of content data being displayed according to the first display mode is selected as the content data of interest, the candidate for metadata related to a date of the content data of interest, and displays, when one of the plurality of content data being displayed according to the second display mode is selected as the content data of interest, the candidate for metadata related to position information of the content data of interest.