1. A document management apparatus capable of managing a plurality of documents in which attribute names and attribute values corresponding to the attribute names are set as attributes, the document management apparatus comprising: a memory that stores a computer program; and at least one processor that executes the computer program to function as: an attribute display unit configured to display, in an attribute display screen, attribute names and attribute values which have been set for one document selected from the plurality of documents based on a user's instruction, wherein the attribute display unit does not display, in the attribute display screen, attribute values which have not been set for the selected one document, a selection unit configured to select, based on a user's instruction, at least one attribute value from the attribute values displayed in the attribute display screen by the attribute display unit, a search screen display unit configured to display, when an instruction to display a search screen is issued in a state where the at least one attribute value is selected in the attribute display screen by the selection unit, the search screen in a state where the selected at least one attribute value and at least one attribute name corresponding to the selected at least one attribute value are set automatically as search conditional expression values and search conditional expression names in a search conditional expression of an attribute search in the search screen, wherein an attribute value that is not selected by the selection unit is not set automatically as a search conditional expression of the attribute search in the search screen displayed by the search screen display unit, wherein the search screen is different from the attribute display screen, and wherein the search screen display unit displays, if a plurality of attribute values are selected by the selection unit, the search screen which includes a plurality of lines for which the selected plurality of attribute values and a plurality of attribute names corresponding to the selected plurality of attribute values are set automatically, wherein each of the plurality of lines is for setting a search conditional expression, a setting unit configured to further add to and/or revise, based on a user's instruction, the search conditional expression of the attribute search in the search screen displayed by the search screen display unit, and an execution unit configured to execute the attribute search for the plurality of documents based on the search conditional expression being set in the search screen.