The optimization of a refresh cycle is carried out in harmony with the error occurrence state in the memory with the presence of a normal patrol controlling section controlling a normal patrol operation that patrols the memory; an additional patrol controlling section controlling an additional patrol operation that patrols, if a first error in the memory is detected during the normal patrol operation, an error occurring area in which the first error occurs and which is included in the memory; a measuring section (15) measuring, if a second error is detected in the error occurring area during the additional patrol operation, an error frequency representing information of error in the error occurring area; and a refresh cycle adjusting section adjusting the refresh cycle in accordance with the error frequency measured by the measuring section.