Deterioration of performance due to diagnosis processing performed when a failure occurs is prevented.A storage apparatus 10 includes a controller 11A and a plurality of expanders 112A, 121A coupled to the controller 11A to form a first system, and includes a controller 11B and a plurality of expanders 112B, 121B coupled to the controller 11B to form a second system. The controller 11A accesses the storage drive 171 through the expanders 112A, 121A, and the second controller 11B accesses the storage drive through the expanders 112B, 121B. In the storage apparatus 10, the controller 11A stores a maximum number (concurrently-executable maximum number) of communication ports 80 that are concurrently diagnosable in the first system, and repeatedly executes a process of selecting the communication ports 80 not exceeding the concurrently-executable maximum number and a process of causing the expanders 112A, 121A to diagnose the selected communication ports 80.