A failure detection method enabling the detection of I/O bus failure and address parity error when installing I/O controllers connected to a system bus in a computer system, and also enabling failure location when installing units in slave/master relationships (e.g. SCSI controller and disk storage units) and when installing an additional slave in a computer system, thus improving the reliability of the system. The failure detection method comprises the steps of executing an instruction which involves providing I/O bus access to a memory to be used by an I/O controller after installed, determining that there is no failure when predetermined results are obtained with the instruction, and installing the I/O controller in the system. When the I/O controller has slave/master relationships with a plurality of slave units, the failure detection method further comprises the steps of detecting a failure in the slave units on the occasion of the installation, and notifying the host processor of the slave unit having the failure.