To provide a disk control system in which the fault of a disk control part can be detected, and access can be performed to a disk device even when one disk control part breaks down.

Disk controllers 7 and 8 which control access to a disk device 11 after receiving an instruction for input and output from a CPU 2 are duplexed, and the disk controller 7 and 8 mutually input data through first and second paths 9 and 10, and compare the data of their own device with the data of the other device. When the compared result is incoincident, the result is communicated to the CPU 2, and the CPU 2 operates the fault diagnosis of the duplexed disk controllers 7 and 8, suppress writing access from the disk controller in which failure is detected to the disk device, and operates data writing from the normal disk controller to the disk device.