A lens apparatus is disclosed, which is capable of keeping the engagement of a protruding portion of a first member and a cam groove portion of a second member even if an external force acts on the apparatus. The lens apparatus comprises: a first member including first and second protruding portions; and a second member including a first groove portion with which the first protruding portion engages, and a second groove portion into which the second protruding portion is inserted. The second protruding portion and the second groove portion are away from each other in a case where the first and second members are located in a specified positional relationship, and come into contact with each other in a case where the first and second members are located in another positional relationship.