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 2 to be managed are divided between a direct collection group comprised of some managed devices 2 whose device-condition information are collected by detecting operation by a portable (mobile) unit 4 for device condition detection on each one of these managed devices 2 and an indirect collection group 8a, 8b comprised of the other managed devices 2 whose device-condition information are collected by communication between each one of these managed devices 2 and a stationary unit 5, 6 disposed to be capable of detecting the device-condition information of the device 2.