Accurate device-condition information of and relating to a number of devices to be managed are collected in an efficient manner. The number of devices to be managed are divided between a direct collection group comprised of some managed devices whose device-condition information are collected by detecting operation by a portable (mobile) unit for device condition detection on each one of these managed devices and an indirect collection group comprised of the other managed devices whose device-condition information are collected by communication between each one of these managed devices and a stationary unit disposed to be capable of detecting the device-condition information of the device.