A lens apparatus attachable to and detachable from a camera body , the lens apparatus comprising: an optical system including a plurality of lens units configured to move in adjusting an in-focus state of a subject image; detection means configured to detect a position of each of the plurality of lens units ; acquisition means configured to acquire position information regarding a single position representing a position of a virtual composite lens unit, that integrates the plurality of lens units into one, corresponding to a current subject distance, based on: the positions of the plurality of lens units detected by the detection means , first relational information indicating a relation between a position of each of the plurality of lens units and a subject distance, and second relational information indicating a relation between the subject distance and a position of the virtual composite lens unit; and control means configured to control the positions of the plurality of lens units based on the position information, wherein the acquisition means is configured to calculate a deviation in the position of the virtual composite lens from a target position of the virtual composite lens corresponding to a target subject distance resulting from a lag in movement of at least one but not all of the plurality of lens units such that at least one but not all of the lens units are at their target position, and to determine the current subject distance based on the deviation. an optical system including a plurality of lens units configured to move in adjusting an in-focus state of a subject image; detection means configured to detect a position of each of the plurality of lens units ; acquisition means configured to acquire position information regarding a single position representing a position of a virtual composite lens unit, that integrates the plurality of lens units into one, corresponding to a current subject distance, based on: the positions of the plurality of lens units detected by the detection means , first relational information indicating a relation between a position of each of the plurality of lens units and a subject distance, and second relational information indicating a relation between the subject distance and a position of the virtual composite lens unit; and the positions of the plurality of lens units detected by the detection means , first relational information indicating a relation between a position of each of the plurality of lens units and a subject distance, and second relational information indicating a relation between the subject distance and a position of the virtual composite lens unit; and control means configured to control the positions of the plurality of lens units based on the position information, wherein the acquisition means is configured to calculate a deviation in the position of the virtual composite lens from a target position of the virtual composite lens corresponding to a target subject distance resulting from a lag in movement of at least one but not all of the plurality of lens units such that at least one but not all of the lens units are at their target position, and to determine the current subject distance based on the deviation. <EOS>