A storage apparatus capable of achieving both an improvement in efficiency of data transfer processing and an improvement in availability and a method of controlling the storage apparatus are provided. A storage apparatus which includes a storage medium for providing an external apparatus with a data storage area includes: a processing unit including multiple processors which execute synchronous processing and asynchronous processing other than the synchronous processing, the synchronous processing being processing to be executed immediately in response to data I/O requests from the external apparatus, the asynchronous processing being processing to be executed as needed in response to a processing request generated in the storage apparatus; a temporary storage unit which provides a storage area where any of the processors temporarily stores write target data in accordance with a data write request among the data I/O requests; and a processor operating rate management part which manages a time schedule for each of the multiple processors to execute the synchronous processing or the asynchronous processing. In the storage apparatus, the processor operating rate management part acquires execution pro-portions of the synchronous processing and the asynchronous processing executed by each of the multiple processors in a past predetermined time period and an usage state of the temporary storage unit used by the multiple processors, compares the acquired execution proportions and the usage state with execution proportions of the synchronous processing, the asynchronous processing, and intensive writing processing set in advance for each of the processors, the intensive writing processing being processing of writing from the temporary storage unit to the storage medium, the execution proportion of the intensive writing processing defined corresponding to the usage state of the temporary storage unit, and sets an operation schedule of the multiple processors in such a way that at least one of the processors executes the synchronous processing at any point in a predetermined execution proportion management unit time.