A diagnosis method executed by a processor includes receiving signal data at a timing of a first clock signal; setting a diagnosis period to perform a diagnosis of a memory with a predetermined period; executing a write operation and a read operation of the signal data on the memory at a timing of a second clock signal that is higher in rate than the first clock signal within the diagnosis period; executing at least one of operations included in the diagnosis of the memory using diagnosis data at a timing of the second clock signal during a period responsive to a difference between a number of first clock pulses of the first clock signal within the diagnosis period and a number of second clock pulses of the second clock signal within the diagnosis period; and diagnosing the memory by repeating the diagnosis period by a plurality of times.